Color filter

ABSTRACT

A process for adjusting the energy of an imaging laser for imaging of a thermally imageable element and thermally imageable elements suitable for this purpose are described, which is useful for color filters and liquid crystal display devices. The process comprises the steps of: (a) providing an imaging unit having a non-imaging laser and an imaging laser, the non-imaging laser having a light detector which is in communication with the imaging laser; (b) contacting a receiver element with the thermally imageable element in the imaging unit, wherein the thermally imageable element comprises a light attenuated layer having a front surface and a back surface; (c) actuating the non-imaging laser to expose the thermally imageable element and the receiver element to an amount of light energy sufficient for the light detector to detect the amount of light reflected from the light attenuated layer of the thermally imageable element; and (d) actuating the imaging laser to focus the imaging laser in order to expose the thermally imageable element to an amount of light energy sufficient for imaging the thermally imageable element. The light attenuation is achieved by use of a light attenuating agent or by physically roughening a base element of the thermally imageable element.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation-in-part of PCT/US01/48929 filed on Dec. 14, 2001 and PCT/US01/48930 filed on Dec. 14, 2001 which are based on Provisional Application No. 60/256,242 filed on Dec. 15, 2000 which are incorporated herein by reference in their entiretees.

FIELD OF THE INVENTION

This invention relates to processes and products for effecting laser-induced thermal transfer imaging. More specifically, the invention relates to a modified thermally imageable element and its use in adjusting the focus of the imaging laser for imaging thermally imageable elements which are useful in color filters and liquid crystal display devices.

BACKGROUND OF THE INVENTION

Liquid crystal display (LCD) devices have become increasingly important in displays which require very low consumption of electrical power or where the environment dictates a lightweight, planar, flat surface. For example, LCDs are used in display devices such as wristwatches, pocket and personal computers, and aircraft cockpit displays. When there is a need to incorporate a color display capability into such display devices, a component called a color filter is used. For the device to have color capability, each pixel is aligned with a color area, typically red, green, or blue, of a color filter array. Depending upon the image to be displayed, one or more of the pixel electrodes is energized during display operation to allow full light, no light, or partial light to be transmitted through the color filter area associated with that pixel. The image perceived by a user is a blend of colors formed by the transmission of light through adjacent color filter areas.

A major contributor to the cost of color LCD devices is the color filter. Four color filter manufacturing methods are known in the art, viz., dye gelatin, pigmented photoresist, electrodeposition and printing. The pigmented photoresist method offers the best trade-off of degradation resistance, optical properties, and flexibility along with high resolution, and is generally preferred. While conventional photolithographic materials and methods may be employed in the photoresist method, it suffers from the high cost and inconvenience associated with numerous process steps, some involving wet chemistry.

Laser-induced thermal transfer processes are well known in applications such as color proofing, electronic circuits, color filters, liquid crystal display devices, and lithography. Such laser-induced processes include, for example, dye sublimation, dye transfer, melt transfer, and ablative material transfer.

Laser-induced processes use a laserable assemblage comprising (a) a thermally imageable element that contains a thermally imageable layer, the exposed areas of which are transferred, and (b) a receiver element having an image receiving layer that is in contact with the thermally imageable layer. The laserable assemblage is imagewise exposed by a laser, usually an infrared laser, resulting in transfer of exposed areas of the thermally imageable layer from the thermally imageable element to the receiver element. The (imagewise) exposure takes place only in a small, selected region of the laserable assemblage at one time, so that transfer of material from the thermally imageable element to the receiver element can be built up one region at a time. The region may be a pixel, some portion of a pixel, or a number of pixels. Computer control produces transfer with high resolution and at high speed.

The equipment used to image thermally imageable elements is comprised of an imaging laser, and a non-imaging laser, wherein the non-imaging laser has a light detector that is in communication with the imaging laser. Since the imaging and non-imaging lasers have emissions at different wavelengths, problems occur with the proper focus of the imaging laser.

A need exists for a process for adjusting the focus of the imaging laser for imaging a thermally imageable element.

SUMMARY OF THE INVENTION

The invention provides a thermal imaging process that uses modified thermally imageable elements that improve the adjusting of the focus of an imaging laser in imaging thermally imageable elements. The invention greatly modifies the imaging latitude of the thermally imageable element by facilitating laser focus and imaging from color to color.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a thermally imageable element (10) useful in the invention having a support (11); a base element having a coatable surface comprising an optional ejection layer or subbing layer (12) an optional heating layer (13); and a thermally imageable colorant-containing layer (14).

FIG. 2 illustrates a receiver element (20), optionally having a roughened surface, useful in the invention having a receiver support (21) and a image receiving layer (22).

FIGS. 3 and 4 illustrate the positioning of the thermally imageable element having a light attenuated layer (10), the receiver element (20), and the optional carrier element 71 on drum (70) prior to vacuum drawdown and laser imaging. A light attenuating agent produces an attenuation of the light.

FIG. 5 illustrates a non-imaging autofocus probe beam light as it is reflected from the thermally imageable element, the receiver element and the carrier element (71) wherein the thermally imageable element does not contain a light attenuated layer.

FIG. 6 illustrates a non-imaging autofocus probe beam light as it is reflected from the thermally imageable element, the receiver element and the carrier element (71), wherein the thermally imageable element contains a light attenuated support, and wherein the light attenuating agent is an absorber.

FIG. 7 illustrates a non-imaging autofocus probe beam light as it is reflected from the thermally imageable element, and the receiver element, wherein the thermally imageable element contains a light attenuated support, and wherein the light attenuating agent is a diffuser.

DETAILED DESCRIPTION OF THE INVENTION

Processes and products for laser induced thermal transfer imaging of thermally imageable elements are disclosed wherein thermally imageable assemblages providing modified imaging characteristics are provided. The thermally imageable assemblages are used in color filters, liquid crystal display devices, and other products described in further detail.

Before the processes of this invention are described in further detail, several different exemplary laserable assemblages made up of the combination of a receiver element, optionally having a roughened surface and a thermally imageable element will be described. The processes of this invention are fast and are typically conducted using one of these exemplary laserable assemblages.

Imageable Element

As shown in FIG. 1, an exemplary thermally imageable element useful for thermal imaging in accordance with the processes of this invention comprises a thermally imageable layer, which typically in a proofing application is a colorant-containing layer (14) and a base element having a coatable surface which comprises an optional ejection layer or subbing layer (12) and optionally a heating layer (13). Each of these layers has separate and distinct functions. Optionally, a support for the thermally imageable element (11) may also be present. In one embodiment, the optional heating layer (13) may be present directly on the support (11). Alternately, an overcoat layer may also be provided on the thermally imageable colorant-containing layer (14).

The thermally imageable element may be simply a laser imageable element for a laser imaging process capable of imaging an imageable element as described herein by non-thermal methods.

The light attenuated layer may be any layer in the thermally imageable element. Light attenuation occurs due to the presence of a light attenuating agent in the light attenuated layer. Typically, the light attenuating agent is not present in the final image; i.e. either the light attenuated layer is removed, typically peeled off, prior to the final image being formed or the light attenuating agent is bleached from the final image so it does not impart unwanted color to the final image. Typically, the light attenuated layer is the support, a release or cushion layer or an ejection or subbing layer.

The light attenuating agent may be selected from the group consisting of an absorber, a diffuser, and mixtures thereof. Depending on the range at which the non-imaging laser operates, such as about 300 nm to about 1500 nm, the absorbers and diffusers should be selected to operate in the same range. Depending on the wavelength range at which the imaging laser operates, which can be from about 300 nm to about 1500 nm, the absorbers and diffusers can be inoperable in the same range. For example, if the non-imaging laser operates in about the 670 nm region and the imaging laser at 830 nm, it is preferred that the absorbers and diffusers operate to absorb or diffuse light in the 670 nm region and the ability of these materials to absorb or diffuse light at 830 nm can be poor. Some examples of light absorbers include any blue phthalocyanine pigments with significant absorption in about the 670 nm range and minimal absoption at 830 nm; such as C.I. Pigment Blue 15 or 15-3, and universally absorbing black pigments such as any carbon black. Some examples of light diffusers are materials which scatter light or scatter and absorb light. They can include white pigments such as titanium dioxide, or combinations (extensions) of white pigments such as: titanium dioxide, barium sulfate, calcium carbonate, oxides, sulfates, carbonates of silicon (i.e. silicon dioxide) and magnesium, etc. Commercial examples of white pigments would include DuPont's TiPure® grades of titanium dioxide. Carbon black examples include any Monarch®, Regal®, Elftex® or Sterling® carbon blacks from Cabot Corporation, Boston, Mass. Blue pigment examples would be the Sunfast® blue pthalocyanine pigment 15-3 series from Sun Chemical Corporation, Cincinnati, Ohio.

The use of dyes or combinations of dyes could also conceivably be employed to affect the imaging properties of the herein described thermal imaging system. To one skilled in the art, combinations of blue, red and green dyes could be substituted for pigments. However, a disadvantage in using dyes is the lack of light fastness and tendency to migrate out of the layer.

Typically, when the light attenuating agent is used in a thermoplastic base element it is incorporated by compounding with the thermoplastic composition of the base element. To those skilled in the art, the compounding techniques can range from the use of Banbury mixers or two roll mills, melt extrusion via a single/twin screw extrusion equipment or solvent dispersion with high shear mixing. All these compounding techniques could be used; however, the preferred method for its ease and simplicity is melt extrusion.

Alternatively, the light attenuated layer can be applied by coating techniques. The coating composition can comprise a dispersion of the light attenuating agent in a binder. A suitable binder can be polymeric and can be the same as the polymers employed in the thermally imageable layer. A minor amount of a surfactant can also be employed. Typically, the binder is a copolymer of methylmethacrylate and n-butylmethacrylate and the surfactant is a fluoropolymer. Usually, the components of the light attenuated layer are mixed into an aqueous dispersion which is applied as a coating by conventional techniques and dried.

The light attenuating agent is combined with the binder and other components of the layer composition in an amount effective to absorb or diffuse the light from the non imaging laser. When the light attenuated layer is made from a coatable composition, the proportion of the polymer used can be the same as that used in the thermally imageable layer. The light attenuating agent is used in the light attenuated layer in an amount sufficient to achieve an absorbance ranging from about 0.1 to about 2.0, typically from about 0.3 to about 0.9 even more typically about 0.6. The absorbance is a dimensionless figure which is well known in the art of spectroscopy. At an absorbance above about 2.0 the base is likely to be too highly absorbing for the imaging process and below about 0.1 there might not be a sufficient attenuating effect.

Base Element:

Typically, the base element (12) is a thick (400 gauge) coextruded polyethylene terephthalate film. Alternately, the base element may be polyester film, specifically polyethylene terephthalate that has been plasma treated to accept the heating layer such as the MELINEX® line of polyester films made by DuPontTeijinFilms™ a joint venture of DuPont and Teijin Limited. When the base element is plasma treated, a subbing layer or ejection layer is usually not provided on the support. Backing layers may optionally be provided on the support. These backing layers may contain fillers to provide a roughened surface on the back side of the base element, i.e. the side opposite from the base element (12). Alternatively, the base element itself may contain fillers, such as silica, to provide a roughened surface on the back surface of the base element. Alternately, the base element may be physically roughened to provide a roughened surface on one or both surfaces of the base element said roughening being sufficient to scatter the light emitted from the non-imaging laser. Some examples of physical roughening methods include sandblasting, impacting with a metal brush, etc. If a support is employed it may be the same or different from the base element. A light attenuated layer may result from a roughened base element surface or surface layer which can also include a light attenuating agent such as an absorber or diffuser. Typically, the support is a thick polyethylene terephthalate film.

Metallized polyester films can be used especially as a base element (12) for a color filter. Specific examples include single or multilayer polyester films such as polyethylene terephthalate or polyolefin films. The base element for color filter applications can range in thickness from about 1 to 4 mils. Useful polyethylene terephthalate films include MELINEX® 473 (4 mil thickness), MELINEX® 6442 (4 mil thickness), MELINEX® LJX111 (1 mil thickness), and MELINEX® 453 (2 mil thickness), all metallized to 50% visible light transmission with metallic chromium by CP Films, Martinsville, Va.

Ejection or Subbing Layer:

The optional ejection layer, which is usually flexible, or optional subbing layer, which may be on one side of the base element (12), as shown in FIG. 1, is the layer that provides the force to effect transfer of the thermally imageable colorant-containing layer to the receiver element in the exposed areas. When heated, this layer decomposes into gaseous molecules providing the necessary pressure to propel or eject the exposed areas of the thermally imageable colorant-containing layer onto the receiver element. This is accomplished by using a polymer having a relatively low decomposition temperature (less than about 350° C., typically less than about 325° C., and more typically less than about 280° C.). In the case of polymers having more than one decomposition temperature, the first decomposition temperature should be lower than 350° C. Furthermore, in order for the ejection layer to have suitably high flexibility and conformability, it should have a tensile modulus that is less than or equal to about 2.5 Gigapascals (GPa), specifically less than about 1.5 GPa, and more specifically less than about 1 Gigapascal (GPa). The polymer chosen should also be one that is dimensionally stable. If the laserable assemblage is imaged through the ejection layer, the ejection layer should be capable of transmitting the laser radiation, and not be adversely affected by this radiation.

Examples of suitable polymers for the ejection layer include (a) polycarbonates having low decomposition temperatures (Td), such as polypropylene carbonate; (b) substituted styrene polymers having low decomposition temperatures, such as poly(alpha-methylstyrene); (c) polyacrylate and polymethacrylate esters, such as polymethylmethacrylate and polybutylmethacrylate; (d) cellulosic materials having low decomposition temperatures (Td), such as cellulose acetate butyrate and nitrocellulose; and (e) other polymers such as polyvinyl chloride; poly(chlorovinyl chloride) polyacetals; polyvinylidene chloride; polyurethanes with low Td; polyesters; polyorthoesters; acrylonitrile and substituted acrylonitrile polymers; maleic acid resins; and copolymers of the above. Mixtures of polymers can also be used. Additional examples of polymers having low decomposition temperatures can be found in U.S. Pat. No. 5,156,938. These include polymers which undergo acid-catalyzed decomposition. For these polymers, it is frequently desirable to include one or more hydrogen donors with the polymer.

Specific examples of polymers for the ejection layer are polyacrylate and polymethacrylate esters, low Td polycarbonates, nitrocellulose, poly(vinyl chloride) (PVC), and chlorinated poly(vinyl chloride) (CPVC). Most specifically are poly(vinyl chloride) and chlorinated poly(vinyl chloride).

Other materials can be present as additives in the ejection layer as long as they do not interfere with the essential function of the layer. Examples of such additives include coating aids, flow additives, slip agents, antihalation agents, plasticizers, antistatic agents, surfactants, and others which are known to be used in the formulation of coatings.

Alternately, a subbing layer may optionally be applied onto the base element (12) in place of the ejection layer resulting in a thermally imageable element having in order at least one subbing layer on one side of the base element (12), at least one heating layer (13), and at least one thermally imageable colorant-containing layer (14). Some suitable subbing layers include polyurethanes, polyvinyl chloride, cellulosic materials, acrylate or methacrylate homopolymers and copolymers, and mixtures thereof. Other custom made decomposable polymers may also be useful in the subbing layer. Specifically useful as subbing layers for polyester, specifically polyethylene terephthalate, are acrylic subbing layers. The subbing layer may have a thickness of about 100 to about 1000 A.

Heating Layer

The optional heating layer (13), as shown in FIG. 1, is deposited on the flexible ejection or subbing layer. The function of the heating layer is to absorb the laser radiation and convert the radiation into heat. Materials suitable for the layer can be inorganic or organic and can inherently absorb the laser radiation or include additional laser-radiation absorbing compounds.

Examples of suitable inorganic materials are transition metal elements and metallic elements of Groups IIIA, IVA, VA, VIA, VIIIA, IIB, IIIB, and VB of the Period Table of the Elements (Sargent-Welch Scientific Company (1979)), their alloys with each other, and their alloys with the elements of Groups IA and IIA. Tungsten (W) is an example of a Group VIA metal that is suitable and which can be utilized. Carbon (a Group IVB nonmetallic element) can also be used. Specific metals include Al, Cr, Sb, Ti, Bi, Zr, Ni, In, Zn, and their alloys and oxides. TiO₂ may be employed as the heating layer material.

The thickness of the heating layer is generally about 10 Angstroms to about 0.1 micrometer, more specifically about 20 to about 60 Angstroms.

Although it is typical to have a single heating layer, it is also possible to have more than one heating layer, and the different layers can have the same or different compositions, as long as they all function as described above. The total thickness of all the heating layers should be in the range given above.

The optical density of the heating layer at the wavelength of the non-imaging laser is typically in the order of greater than about 0.1 and less than about 1.0 transmission density.

The heating layer(s) can be applied using any of the well-known techniques for providing thin metal layers, such as sputtering, chemical vapor deposition, and electron beam.

Thermally Imageable Layer:

The thermally imageable layer, which in a color proofing application is typically a thermally imageable colorant-containing layer (14) is formed by applying a thermally imageable composition, typically containing a colorant, to a base element. For other applications, such as electronic circuit applications, the thermally imageable layer may not contain a colorant. For these applications, the thermally imageable element may contain electronically active conductors, insulators, semiconductors, or precursors to these functions.

When the thermally imageable layer is a colorant-containing layer it comprises (i) a polymeric binder which is different from the polymer in the ejection layer, and (ii) a colorant comprising a dye or a pigment dispersion.

The binder for the colorant-containing layer is a polymeric material having a decomposition temperature that is greater than about 250° C. and specifically greater than about 350° C. The binder should be film forming and coatable from solution or from a dispersion. Binders having melting points less than about 250° C. or plasticized to such an extent that the glass transition temperature is less than about 70° C. are typical. However, heat-fusible binders, such as waxes should be avoided as the sole binder since such binders may not be as durable, although they are useful as cobinders in decreasing the melting point of the top layer.

It is typical that the polymer of the binder does not self-oxidize, decompose or degrade at the temperature achieved during the laser exposure so that the exposed areas of the thermally imageable layer comprising colorant and binder, are transferred intact for improved durability. Examples of suitable binders include copolymers of styrene and (meth)acrylate esters, such as styrene/methyl-methacrylate; copolymers of styrene and olefin monomers, such as styrene/ethylene/butylene; copolymers of styrene and acrylonitrile; fluoropolymers; copolymers of (meth)acrylate esters with ethylene and carbon monoxide; polycarbonates having higher decomposition temperatures; (meth)acrylate homopolymers and copolymers; polysulfones; polyurethanes; polyesters. The monomers for the above polymers can be substituted or unsubstituted. Mixtures of polymers can also be used.

Specific polymers for the binder of the colorant-containing layer include, but are not limited to, acrylate homopolymers and copolymers, methacrylate homopolymers and copolymers, (meth)acrylate block copolymers, and (meth)acrylate copolymers containing other comonomer types, such as styrene.

Specific polymers for the binder of the colorant-containing layer include, but are not limited to, random copolymers of comonomers choosen from methyl methacrylate, n-butyl methacrylate, glycidyl methacrylate, n-butyl acrylate, methacrylic acid, acrylic acid, styrene, and macromonomers. The molecular weight of the specific polymers can be controlled by chain transfer agents such as macromonomers.

The binder polymer generally can be used in a concentration of about 15 to about 50% by weight, based on the total weight of the colorant-containing layer, specifically about 30 to about 40% by weight.

The colorant of the thermally imageable layer may be an image forming pigment which is organic or inorganic. Examples of suitable inorganic pigments include carbon black and graphite. Examples of suitable organic pigments include color pigments such as Rubine F6B (C.I. No. Pigment 184); Cromophthal® Yellow 3G (C.I. No. Pigment Yellow 93); Hostaperm® Yellow 3G (C.I. No. Pigment Yellow 154); Monastral® Violet R (C.I. No. Pigment Violet 19); 2,9-dimethylquinacridone (C.I. No. Pigment Red 122); Indofast® Brilliant Scarlet R6300 (C.I. No. Pigment Red 123); Quindo Magenta RV 6803; Monastral® Blue G (C.I. No. Pigment Blue 15); Monastral® Blue BT 383D (C.I. No. Pigment Blue 15); Monastral® Blue G BT 284D (C.I. No. Pigment Blue 15); and Monastral® Green GT 751D (C.I. No. Pigment Green 7). Combinations of pigments and/or dyes can also be used. For color filter array applications, high transparency pigments (that is at least about 80% of light transmits through the pigment) are typical, having small particle size (that is about 100 nanometers).

Pigment dispersions used for preparation of a thermally imageable layer for a color filter can be prepared by dispersing the appropriate pigment using one or more polymeric dispersants in aqueous media. Color filters for LCD display applications require very high transparency (see for instance T. Sugiura, “EBU Color Filters for LCDs”, Society for Information Display, Digest of Technical Papers, 2001, 33, p146-9). In order to meet these transparency requirements, the pigments can be milled during or before the dispersion process to give final pigment particle size distributions with greater than 90% of the particles having diameters less than 200 nm as determined by conventional light scattering methods.

In accordance with principles well known to those skilled in the art, the concentration of pigment will be chosen to achieve the optical density desired in the final image. The amount of pigment will depend on the thickness of the active coating and the absorption of the colorant. Optical densities greater than 0.8 at the wavelength of maximum absorption are typically required. Even higher densities are typical. Optical densities in the 2-3 range or higher are achievable with application of this invention.

The optical density of the pigmented layer at the wavelength of the non-imaging laser may be in the range from greater than about 0.01 to less than about 5.0 transmission density, more typically in the order of about 0.2 to about 3.0 transmission density. This density may not be controlled in selection of the colorants, but the non-imaging laser must be able to accommodate at least this range of optical properties.

A dispersant is usually used in combination with the pigment in order to achieve maximum color strength, transparency and gloss. The dispersant is generally an organic polymeric compound and is used to separate the fine pigment particles and avoid flocculation and agglomeration of the particles. A wide range of dispersants is commercially available. A dispersant will be selected according to the characteristics of the pigment surface and other components in the composition as known by those skilled in the art. However, one class of dispersant suitable for practicing the invention is that of the AB dispersants. The A segment of the dispersant adsorbs onto the surface of the pigment. The B segment extends into the solvent into which the pigment is dispersed. The B segment provides a barrier between pigment particles to counteract the attractive forces of the particles, and thus to prevent agglomeration. The B segment should have good compatibility with the solvent used. The AB dispersants of utility are generally described in U.S. Pat. No. 5,085,698. Conventional pigment dispersing techniques, such as ball milling, sand milling, etc., can be employed.

A specific dispersant useful in this invention is a block copolymer made by group transfer polymerization from benzyl methacrylate and trimethylsilyl methacrylate wherein some or all of the polymerized trimethylsilyl methacrylate is hydrolyzed to produce polymerized methacrylic acid groups.

The pigment is present in an amount of from about 15 to about 95% by weight, typically about 35 to about 65% by weight, based on the total weight of the composition of the colorant-containing layer.

Although the above discussion was directed to color proofing, color filters, and liquid crystal displays, the element and process of the invention apply equally to the transfer of other types of materials in different applications. In general, the scope of the invention is intended to include any application in which solid material is to be applied to a receptor in a pattern. A specific application is the construction of electronic circuitry, wherein the material transferred affects circuit characteristics.

The colorant-containing layer may be coated on the base element from a solution in a suitable solvent, however, it is typical to coat the layer(s) from a dispersion. Any suitable solvent can be used as a coating solvent, as long as it does not deleteriously affect the properties of the assemblage, using conventional coating techniques or printing techniques, for example, gravure printing. A typical solvent is water. The colorant-containing layer may be applied by a coating process accomplished using the WaterProof® Color Versatility Coater sold by DuPont, Wilmington, Del. Coating of the colorant-containing layer can thus be achieved shortly before the exposure step. This also allows for the mixing of various basic colors together to fabricate a wide variety of colors to match the Pantone® color guide currently used as one of the standards in the proofing industry.

Thermal Amplification Additive

A thermal amplification additive is typically present in the thermally imageable colorant-containing layer, but may also be present in the ejection layer(s) or subbing layer.

The function of the thermal amplification additive is to amplify the effect of the heat generated in the heating layer and thus to further increase sensitivity to the laser. This additive should be stable at room temperature. The additive can be (1) a decomposing compound which decomposes when heated, to form gaseous by-products(s), (2) an absorbing dye which absorbs the incident laser radiation, or (3) a compound which undergoes a thermally induced unimolecular rearrangement which is exothermic. Combinations of these types of additives may also be used.

Decomposing compounds of group (1) include those which decompose to form nitrogen, such as diazo alkyls, diazonium salts, and azido (—N3) compounds; ammonium salts; oxides which decompose to form oxygen; carbonates or peroxides. Specific examples of such compounds are diazo compounds such as 4-diazo-N,N′ diethyl-aniline fluoroborate (DAFB). Mixtures of any of the foregoing compounds can also be used.

An absorbing dye of group (2) is typically one that absorbs in the infrared region. Examples of suitable near infrared absorbing NIR dyes which can be used alone or in combination include poly(substituted) phthalocyanine compounds and metal-containing phthalocyanine compounds; cyanine dyes; squarylium dyes; chalcogenopyryioacrylidene dyes; croconium dyes; metal thiolate dyes; bis(chalcogenopyrylo)polymethine dyes; oxyindolizine dyes; bis(aminoaryl)polymethine dyes; merocyanine dyes; and quinoid dyes. When the absorbing dye is incorporated in the ejection or subbing layer, its function is to absorb the incident radiation and convert this into heat, leading to more efficient heating. It is typical that the dye absorbs in the infrared region. For imaging applications, it is also typical that the dye has very low absorption in the visible region.

Absorbing dyes also of group (2) include the infrared absorbing materials disclosed in U.S. Pat. Nos. 4,788,128; 4,942,141 ; 4,948,778; 4,950,639; 5,019,549; 4,948,776; 4,948,777 and 4,952,552.

When present in the colorant-containing layer, the thermal amplification weight percentage is generally at a level of about 0.95-about 11.5%. The percentage can range up to about 25% of the total weight percentage in the colorant-containing layer. These percentages are non-limiting and one of ordinary skill in the art can vary them depending upon the particular composition of the layer.

The colorant-containing layer generally has a thickness in the range of about 0.1 to about 5 micrometers, typically in the range of about 0.1 to about 1.5 micrometers. Thicknesses greater than about 5 micrometers are generally not useful as they require excessive energy in order to be effectively transferred to the receiver.

Although it is typical to have a single colorant-containing layer, it is also possible to have more than one colorant-containing layer, and the different layers can have the same or different compositions, as long as they all function as described above. The total thickness of the combined colorant-containing layers is usually in the range given above.

Additional Additives

Other materials can be present as additives in the colorant-containing layer as long as they do not interfere with the essential function of the layer. Examples of such additives include stabilizers, coating aids, plasticizers, flow additives, slip agents, antihalation agents, antistatic agents, surfactants, and others which are known to be used in the formulation of coatings. However, it is typical to minimize the amount of additional materials in this layer, as they may deleteriously affect the final product after transfer. Additives may add unwanted color for color proofing applications, or they may decrease durability and print life in lithographic printing applications.

Additional Layers

The thermally imageable element may have additional layers. For example, an antihalation layer may be used on the side of the flexible ejection layer opposite the colorant-containing layer. Materials which can be used as antihalation agents are well known in the art. Other anchoring or subbing layers can be present on either side of the flexible ejection layer and are also well known in the art.

In some embodiments of this invention, a material functioning as a heat absorber and a colorant is present in a single layer, termed the top layer. Thus the top layer has a dual function of being both a heating layer and a colorant-containing layer. The characteristics of the top layer are the same as those given for the colorant-containing layer. A typical material functioning as a heat absorber and colorant is carbon black.

An overcoat layer may also be present above the thermally imageable colorant-containing layer. The bleach agent for bleaching the light attenuating agent which may be present in the thermally imageable colorant-containing layer may be present in the overcoat layer. If the light attenuating agent is present in the overcoat layer, the light attenuating agent will have to be brought into contact with the overcoat layer prior to formation of the final element from a different source.

Yet additional thermally imageable elements may comprise alternate colorant-containing layer or layers on a support. Additional layers may be present depending of the specific process used for imagewise exposure and transfer of the formed images. Some suitable thermally imageable elements are disclosed in U.S. Pat. Nos. 5,773,188, 5,622,795, 5,593,808, 5,156,938, 5,256,506, 5,171,650 and 5,681,681.

Receiver Element

The receiver element (20), shown in FIG. 2, is the part of the laserable assemblage, to which the exposed areas of the thermally imageable layer, typically comprising a polymeric binder and a pigment, can be transferred before being transferred to a permanent substrate. In most cases, the exposed areas of the thermally imageable layer will not be removed from the thermally imageable element in the absence of a receiver element. That is, exposure of the thermally imageable element alone to laser radiation does not cause material to be removed, or transferred. The exposed areas of the thermally imageable layer, are removed from the thermally imageable element only when it is exposed to laser radiation and the thermally imageable element is in contact with or adjacent to the receiver element. In one embodiment, the thermally imageable element actually touches the surface of the image receiving layer of the receiver element.

The receiver element (20) may be non-photosensitive or photosensitive.

The non-photosensitive receiver element usually comprises a receiver support (21) and an image receiving layer (22). The receiver support (21) usually comprises a dimensionally stable sheet material. The assemblage can be imaged through the receiver support if that support is transparent. Examples of transparent films for receiver supports include, for example polyethylene terephthalate, polyether sulfone, a polyimide, a poly(vinyl alcohol-co-acetal), polyethylene, or a cellulose ester, such as cellulose acetate. Examples of opaque support materials include, for example, polyethylene terephthalate filled with a white pigment such as titanium dioxide, ivory paper, or synthetic paper, such as Tyvek® spunbonded polyolefin made by E. I. du Pont de Nemours and Company of Wilmington, Del. Paper supports are typical for proofing applications, while a polyester support, such as poly(ethylene terephthalate) is typical for a medical hardcopy and color filter array applications. Roughened supports may also be used in the receiver element. The receiver support may be multilayered such as a polyester film with a polyacetate coating for example an ethylene vinyl acetate copolymer.

Glass or glass with a photolithographically produced mask can be a receiver support for a color filter. A specific embodiment of a receiver element is an image receiving layer on a photolithographically produced mask on a glass sheet. In this embodiment, the photolithographically produced mask on a glass sheet is also a permanent substrate. The image receiving layer can be placed on a receiver support such as glass or glass with a photolithographically produced mask by methods such as lamination, coating, spin coating, or spraying.

The image receiving layer (22) may comprise one or more layers wherein optionally the outermost layer is comprised of a material capable of being micro-roughened. Some examples of materials that are useful include a polycarbonate; a polyurethane; a polyester; polyvinyl chloride; styrene/acrylonitrile copolymer; poly(caprolactone); poly(vinylacetate), vinylacetate copolymers with ethylene and/or vinyl chloride; (meth)acrylate homopolymers (such as butyl-methacrylate) and copolymers; and mixtures and copolymers thereof.

A specific (meth)acrylate copolymer useful in the image receiving layer is a copolymer of methyl methacrylate, glycidyl methacrylate, n-butyl acrylate, and methacrylic acid. Chain transfer agents are useful to produce polymers and copolymers for the image receiving layer at a desired molecular weight; a specific chain transfer agent for this application is a macromonomer. A useful additive in the image receiving layer is a base. Suitable bases are ammonia and N,N-dimethylethanolamine. Surfactants are useful ingredients in the image receiving layer. A specific example of a useful surfactant is a fluorosurfactant, such as CAS # [57534-45-7], ZONYL® FSA (DuPont, Wilmington, Del.).

A specific outermost image receiving layer is a crystalline polymer or poly(vinylacetate) layer. The crystalline image receiving layer polymers, for example, polycaprolactone polymers, typically have melting points in the range of about 50 to about 64° C., more typically about 56 to about 64° C., and most typically about 58 to about 62° C. Blends made from 5-40% Capa® 650 (melt range 58-60° C.) and Tone® P-300 (melt range 58-62° C.), both polycaprolactones, are particularly useful as the outermost layer in this invention. Typically, 100% of CAPA 650 or Tone P-300 is used. However, thermoplastic polymers, such as polyvinyl acetate, have higher melting points (softening point ranges of about 100 to about 180° C.). Useful receiver elements are also disclosed in U.S. Pat. No. 5,534,387 wherein an outermost layer optionally capable of being micro-roughened, for example, a polycaprolactone or poly(vinylacetate) layer is present on the ethylene/vinyl acetate copolymer layer disclosed therein. The ethylene/vinyl acetate copolymer layer thickness can range from about 0.5 to about 5 mils and the polycaprolactone layer thickness from about 2 to about 100 mg/dm². Typically, the ethylene/vinyl acetate copolymer comprising more ethylene than vinyl acetate.

One preferred example is the WaterProof® Transfer Sheet sold by DuPont under Stock #G06086 having coated thereon a polycaprolactone or poly(vinylacetate) layer. This image receiving layer can be present in any amount effective for the intended purpose. In general, good results have been obtained at coating weights in the range of about 5 to about 150 mg/dm², typically about 20 to about 60 mg/dm².

The image receiving layer or layers described above may optionally include one or more other layers between the receiver support and the image receiving layer. A useful additional layer between the image receiving layer and the support is a release layer. The receiver support alone or the combination of receiver support and release layer is referred to as a first temporary carrier. The release layer can provide the desired adhesion balance to the receiver support so that the image-receiving layer adheres to the receiver support during exposure and separation from the thermally imageable element, but promotes the separation of the image receiving layer from the receiver support in subsequent steps. Examples of materials suitable for use as the release layer include polyamides, silicones, vinyl chloride polymers and copolymers, vinyl acetate polymers and copolymers and plasticized polyvinyl alcohols. The release layer can have a thickness in the range of about 1 to about 50 microns.

A cushion layer which is a deformable layer may also be present in the receiver element, typically between the release layer and the receiver support. The cushion layer may be present to increase the contact between the receiver element and the thermally imageable element when assembled. Additionally, the cushion layer aids in the optional micro-roughening process by providing a deformable base under pressure and optional heat. Furthermore, the cushion layer provides excellent lamination properties in the final image transfer to a paper or other substrate. Examples of suitable materials for use as the cushion layer include copolymers of styrene and olefin monomers; such as, styrene/ethylene/butylene/styrene, styrene/butylene/styrene block copolymers, ethylene-vinylacetate and other elastomers useful as binders in flexographic plate applications. The cushion layer may have a thickness range from about 0.5 to about 5 mils (or higher).

Methods for optionally roughening the surface of the image receiving layer include micro-roughening. Micro-roughening may be accomplished by any suitable method. One specific example, is by bringing it in contact with a roughened sheet typically under pressure and heat. The pressures used may range from about 800+/− about 400 psi. Optionally, heat may be applied up to about 80 to about 88° C. (175 to 190° F.) more typically about 54.4° C. (130° F.) for polycaprolactone polymers and about 94° C. (200° F.) for poly(vinylacetate) polymers, to obtain a uniform micro-roughened surface across the image receiving layer. Alternatively, heated or chilled roughened rolls may be used to achieve the micro-roughening.

It is typical that the means used for micro-roughening of the image receiving layer has a uniform roughness across its surface. Typically, the means used for micro-roughening has an average roughness (Ra) of about 1 μ and surface irregularities having a plurality of peaks, at least about 20 of the peaks having a height of at least about 200 nm and a diameter of about 100 pixels over a surface area of about 458 μ by about 602 μ.

The roughening means should impart to the surface of the image receiving layer an average roughness (Ra) of less than about 1 μ, typically less than about 0.95 μ, and more typically less than about 0.5 μ, and surface irregularities having a plurality of peaks, at least about 40 of the peaks, typically at least about 50 of the peaks, and still more typically at least about 60 of the peaks, having a height of at least about 200 nm and a diameter of about 100 pixels over a surface area of about 458 μ by about 602 μ These measurements are made using Wyco Profilometer (Wyko Model NT 3300) manufactured by Veeko Metrology, Tucson, Ariz.

The outermost surface of the receiver element may further comprise a gloss reading of about 5 to about 35 gloss units, typically about 20 to about 30 gloss units, at an 85° angle. A GARDCO 20/60/85 degree NOVO-GLOSS meter manufactured by The Paul Gardner Company may be used to take measurements. The glossmeter should be placed in the same orientation for all readings across the transverse direction orientation.

The topography of the surface of the image receiving layer may be important in obtaining a high quality final image with substantially no micro-dropouts.

The receiver element is typically an intermediate element in the process of the invention because the laser imaging step is normally followed by one or more transfer steps by which the exposed areas of the thermally imageable layer are transferred to the permanent substrate. However, it can be advantageous, especially in the making color filters, to omit the transfer steps and instead image directly onto the permanent substrate or onto the image receiving layer of a receiving element which includes the permanent substrate as the receiver support.

Permanent Substrate

One advantage of the process of this invention is that the permanent substrate for receiving the colorant-containing image can be chosen from almost any sheet material desired. For most proofing applications a paper substrate is used, typically the same paper on which the image will ultimately be printed. Most any paper stock can be used. An example of a paper substrate is LOE paper. However, almost any paper stock can be used. Other materials which can be used as the permanent substrate include cloth, wood, glass, china, most polymeric films, synthetic papers, thin metal sheets or foils, etc. Almost any material which will adhere to the thermoplastic polymer layer, can be used as the permanent substrate. For color filter applications the permanent substrate can be glass or glass with a photolithographically produced mask. A permanent substrate can also be modified by placing a receiving layer on it, and thereafter imaging to that receiving layer using a thermally imageable element. The combination of a permanent substrate and a receiving layer can serve as a receiver element (20). A specific embodiment of such a receiver element is formed by lamination of a receiver layer to glass or to glass having a photolithographically-applied mask defining transparent pixel regions in a color filter.

Autofucus Process Steps

The process for adjusting the energy of an imaging laser for imaging a thermally imageable element comprises the steps of:

(a) providing an imaging unit having a non-imaging laser and an imaging laser, the non-imaging laser having a light detector which is in communication with the imaging laser;

(b) contacting a receiver element with the thermally imageable element in the imaging unit, wherein the thermally imageable element comprises a light attenuated layer having a front surface and a back surface;

(c) actuating the non-imaging laser to expose the thermally imageable element and the receiver element to an amount of light energy sufficient for the light detector to detect the amount of light reflected from the light attenuated layer of the thermally imageable element and the receiver element, whereby light reflected from interfaces beyond the back surface of the light attenuated layer is substantially reduced and is substantially dominated by the light reflecting from the light attenuated layer of the thermally imageable element into the light detector; and

(d) actuating the imaging laser to properly focus the imaging laser in order to expose the thermally imageable element to an amount of light energy sufficient for imaging the thermally imageable element, the focus of light energy being determined by the amount of light reflected from the light attenuated layer of the thermally imageable element and communicated to the imaging laser by the light detector.

The imaging unit has a non-imaging laser and an imaging laser, the non-imaging laser having a light detector which is in communication with the imaging laser. Typically the non-imaging laser emits in about the 300 nm to about the 1500 nm region. The non-imaging laser is not used to image the thermally imageable element, and is therefore constantly operational prior to and during imaging for focussing the imaging laser thereby adjusting the energy to the imaging laser for the imaging step. In one embodiment, the non-imaging laser may emit in the 670 nm region and the imaging laser may emit in about the 750 to 850 nm region. An example of a non-imaging laser is the Toshiba (Japan) 10 mW, 670 nm visible light laser diode. Suitable imaging lasers may be obtained from Spectra Diode Laboratries, San Jose, Calif. or Sanyo Electric Co., Osaka, JP. These may be used as part of a laser-spatial light modulator system such as that disclosed in U.S. Pat. No. 5,517,359, or electrically modulated directly as disclosed in U.S. Pat. No. 4,743,091. Some typically used light detectors, also known as position sensitive detectors include monolithic Silicon detectors comprising 2, 4, or a similar number of elements arrayed such that the portion of reflected beam on each segment can be measured, and the relative position of a feature such as the center of the beam can be determined. Suitable light detectors may be obtained from United Detector Technology (U.S.A.). Alternately, the position of the beam could be determined from a sensor having greater than 4 elements, such as a CCD or CMOS sensor having 1024 to 10,000,000 elements, as used in television image inspection systems. An example is the KAF-0400 from Eastman Kodak Co., Rochester, N.Y. One example of an imaging unit is that disclosed in U.S. Pat. No. 6,137,580.

As shown in FIGS. 3 and 4, the optional carrier element (71), the receiver element (20) having the light attenuated layer, and the thermally imageable element (10) are positioned over a drum (70) which is part of an imaging unit. One example of an imaging unit is the CREO Spectrum Trendsetter which utilizes a loading cassette. The optional carrier element may have a series of holes along the edges of the element as shown to assist in the drawing of a vacuum prior to the imaging step. The thermally imageable element (10), and the receiver element (20) may be loaded into the cassette in this order with an interleaving sheet present between each of the specified elements. At least one additional thermally imageable element (10), may also be loaded into the cassette.

As shown in FIGS. 5, 6 and 7, after contact of the thermally imageable element and the receiver element is achieved, the probe beam light (40) from the non-imaging laser is emitted in the direction of the sandwich formed by the optional carrier element (71), the receiver element (20) and the thermally imageable element (10).

As shown in FIG. 5, wherein the thermally imageable element does not comprise a light attenuated layer, the light reflected off the back surface of the thermally imageable element and seen by light detector (50) is depicted by (41), the light reflected off the receiver element is depicted as (42), and the light reflected off the carrier element is depicted as (43). Those skilled in the art will recognize that each of these reflections may be comprised of individual reflections produced at each interface where the optical properties change, and each reflection will have wavelength dependant amplitude and phase. (51) represents multiple reflected spots from the thermally imageable element (10), the receiver element (20) and the optional carrier element (71) onto the light detector (50).

As shown in FIG. 6, wherein the thermally imageable element comprises a light attenuated layer, wherein the light attenuating agent is an absorber, the light reflected off the receiver element (42) and the carrier element depicted as (43) is substantially reduced. As shown in FIG. 7, wherein the thermally imageable element comprises a light attenuated layer, wherein the light attenuating agent is a diffuser, the light reaching the light attenuating layer in the thermally imageable element is diffused as depicted by (44 a) through (44 e).

The multiple reflected spots (51) could comprise 10 or more individual beams for the optical sandwich depicted in FIG. 3. The light detector, typically a position sensitive detector and its associated electronics and optional processing computer determines the position of the plane onto which to focus the imaging laser light based on these varying signals from the reflected light as the sandwich moves under the imaging system which includes the imaging laser. This determination of the optimum focus position is then communicated to the imaging laser.

The focus position is the distance in microns that the imaging laser beam travels into the thermally imageable element (color donor structure). The distance is measured starting from the outermost surface of the thermally imageable element and ending at the point where the beam reaches either the surface of the metal layer (if present) or the surface of the thermally imageable layer which is closest to the laser. The distance is measured empirically by imaging equipment software. This distance may not correspond exactly to the thicknesses of the layers of the thermally imageable element as measured by conventional means such as a micrometer, because the laser beam does not travel perpendicular to the thermally imageable element. There can be some variation in focus positions for a given set of films as the imaging laser source ages and when films of the same color have different thicknesses because of non-uniformity of the thicknesses of the layers making up the thermally imageable element. The imaging laser is then actuated to focus the imaging laser in order to expose the thermally imageable element to an amount of light energy sufficient for imaging the thermally imageable element, the focus of light energy being determined by the amount of light reflected from the light attenuated layer of the thermally imageable element and the receiver element and communicated to the imaging laser by the light detector. Where one or more of the reflected non-imaging beams is spurious or otherwise makes determination of the position of the media sandwich erroneous or indeterminate, focusing errors of the imaging beam can occur. Elimination or reduction of reflected light from the interfaces beyond the light attenuated layer have been found to improve the accuracy of determining the proper focusing position for the imaging laser.

An advantage of the invention is consistency in the measurement of surface reflectivity of a imageable donor element, which is a factor in achieving focus consistency. A lower standard deviation of the surface reflectivity measurement is found to be accompanied by improved focus performance, due to partial reflection of the autofocus laser from more than one surface, which leads to highly variable reflectivity values, complicates the determination of the proper focus conditions. A high variability of surface reflectivity, most easily observed in an increased standard deviation of surface reflectivity, is extremely undesirable for proper operation of an imager.

Imaging Process Steps

Exposure

The first step in the process of the invention is imagewise exposing the laserable assemblage to laser radiation. The exposure step is typically effected with an imaging laser at a laser fluence of about 600 mJ/cm² or less, most typically about 250 to about 440 mJ/cm². The laserable assemblage comprises the thermally imageable element and the receiver element.

The assemblage is normally prepared following removal of a coversheet(s), if present, by placing the thermally imageable element in contact with the receiver element such that the thermally imageable layer actually touches the image receiving layer on the receiver element. Vacuum and/or pressure can be used to hold the two elements together. As one alternative, the thermally imageable and receiver elements can be held together by fusion of layers at the periphery. As another alternative, the thermally imageable and receiver elements can be taped together and taped to the imaging apparatus, or a pin/clamping system can be used. As yet another alternative, the thermally imageable element can be laminated to the receiver element to afford a laserable assemblage. The laserable assemblage can be conveniently mounted on a drum to facilitate laser imaging. Those skilled in the art will recognize that other engine architectures such as flatbed, internal drum, capstan drive, etc. can also be used with this invention.

Various types of lasers can be used to expose the laserable assemblage. The laser is typically one emitting in the infrared, near-infrared or visible region. Particularly advantageous are diode lasers emitting in the region of about 750 to about 870 nm which offer a substantial advantage in terms of their small size, low cost, stability, reliability, ruggedness and ease of modulation. Diode lasers emitting in the range of about 780 to about 850 nm are most typical. Such lasers are available from, for example, Spectra Diode Laboratories (San Jose, Calif.). One preferred device used for applying an image to the image receiving layer is the Creo Spectrum Trendsetter 3244F, which utilizes lasers emitting near 830 nm. This device utilizes a Spatial Light Modulator to split and modulate the 5-50 Watt output from the ˜830 nm laser diode array. Associated optics focus this light onto the imageable elements. This produces 0.1 to 30 Watts of imaging light on the donor element, focused to an array of 50 to 240 individual beams, each with 10-200 mW of light in approximately 10×10 to 2×10 micron spots. Similar exposure can be obtained with individual lasers per spot, such as disclosed in U.S. Pat. No. 4,743,091. In this case each laser emits 50-300 mW of electrically modulated light at 780-870 nm. Other options include fibre coupled lasers emitting 500-3000 mW and each individually modulated and focused on the media. Such a laser can be obtained from Opto Power in Tucson, Ariz.

Optical imaging systems can be constructed based on any of these laser options. In each system, focus of the imaging laser can be determined manually or automatically. A common autofocus approach utilizes a separate non-imaging laser incident on the desired imaging plane and reflected into a sensor. There are many approaches to the design of this autofocus system, but they can be incorporated into imaging systems based on any exposure laser source.

The exposure may take place through the optional ejection layer or subbing layer and/or the heating layer of the thermally imageable element. The optional ejection layer or subbing layer or the receiver element having a roughened surface, must be substantially transparent to the laser radiation. The heating layer absorbs the laser radiation and assists in the transfer of the thermally imageable material, e.g. the colorant alone or together with the binder. In some cases, the ejection layer or subbing layer of the thermally imageable element will be a film that is transparent to infrared radiation and the exposure is conveniently carried out through the ejection or subbing layer. In other cases, these layers may contain laser absorbing dyes which aid in material transfer to the image receiving element.

The laserable assemblage is exposed imagewise so that the exposed areas of the thermally imageable layer are transferred to the receiver element in a pattern. The pattern itself can be, for example, in the form of dots or line work generated by a computer, in a form obtained by scanning artwork to be copied, in the form of a digitized image taken from original artwork, or a combination of any of these forms which can be electronically combined on a computer prior to laser exposure. The laser beam and the laserable assemblage are in constant motion with respect to each other, such that each minute area of the assemblage, i.e., “pixel” is individually addressed by the laser. This is generally accomplished by mounting the laserable assemblage on a rotatable drum. A flat bed recorder can also be used.

Separation

The next step in the process of the invention is separating the thermally imageable element from the receiver element. Usually this is done by simply peeling the two elements apart. This generally requires very little peel force, and is accomplished by simply separating the thermally imageable support from the receiver element. This can be done using any conventional separation technique and can be manual or automatic without operator intervention.

A specific method of separating the thermally imageable element from the receiver element is by peeling the thermally imageable element away from the nearly immobile receiving element. Peeling can be done manually, or by manipulating the imaged thermally imageable element over a guide. A specific guide which can be used is a rod. Any direction of peeling can be used. For a specific pattern such as parallel bands of colored thermally transferred material used for a color filter, different directions of peeling with respect to the parallel bands may give different results. Two specific directions of peeling using a rod for a guide are to position the rod either parallel to the long direction of a band or perpendicular. When the rod is positioned parallel to the long direction to guide the peeling, individual bands of thermally transferred material are peeled away from the imaged thermally imageable element essentially one by one. When the rod is positioned perpendicular to the long direction to guide the peeling, bands of thermally transferred material are peeled away from the imaged thermally imageable element essentially bit by bit at the same time for all bands.

Separation results in a laser generated image, such as a color image, typically a halftone dot image, comprising the transferred exposed areas of the thermally imageable layer, being revealed on the image receiving layer of the receiver element. Typically for a color proof the image formed by the exposure and separation steps is a laser generated halftone dot color image formed on a crystalline polymer layer, the crystalline polymer layer being located on a first temporary carrier which may or may not have a layer present directly on it prior to application of the crystalline polymer layer, wherein either the first temporary carrier or the optional layer that may be present directly on it comprise the light attenuating agent.

Additional Steps

The so revealed image on the image receiving layer may then be transferred directly to a permanent substrate or it may be transferred to an intermediate element such as an image rigidification element, and then to a permanent substrate. Typically, the image rigidification element comprises a support having a release surface and a thermoplastic polymer layer.

The so revealed image on the image receiving layer is then brought into contact with, typically laminated to, the thermoplastic polymer layer of the image rigidification element resulting in the thermoplastic polymer layer of the rigidification element and the image receiving layer of the receiver element encasing the image. A WaterProof® Laminator, manufactured by DuPont is preferably used to accomplish the lamination. However, other conventional means may be used to accomplish contact of the image carrying receiver element with the thermoplastic polymer layer of the rigidification element. It is important that the adhesion of the rigidfication element support having a release surface to the thermoplastic polymer layer be less than the adhesion between any other layers in the sandwich. The novel assemblage or sandwich is highly useful, e.g., as an improved image proofing system. The support having a release surface may then removed, typically by peeling off, to reveal the thermoplastic film. The image on the receiver element may then be transferred to the permanent substrate by contacting the permanent substrate with, typically laminating it to, the revealed thermoplastic polymer layer of the sandwich. Again a WaterProof® Laminator, manufactured by DuPont, is typically used to accomplish the lamination. However, other conventional means may be used to accomplish this contact.

Another embodiment includes the additional step of removing, typically by peeling off, the receiver support resulting in the assemblage or sandwich comprising the permanent substrate, the thermoplastic layer, the image, and the image receiving layer. In a more typical embodiment, these assemblages represent a printing proof comprising a laser generated halftone dot color thermal image formed on a crystalline polymer layer, and a thermoplastic polymer layer laminated on one surface to said crystalline polymer layer and laminated on the other surface to the permanent substrate, whereby the color image is encased between the crystalline polymer layer and the thermoplastic polymer layer.

Formation of Multicolor Images

In proofing applications, the receiver element can be an intermediate element onto which a multicolor image is built up. A thermally imageable element having a thermally imageable layer comprising a first pigment is exposed and separated as described above. The receiver element has an image formed with the first pigment, which is typically a laser generated halftone dot color thermal image. Thereafter, a second thermally imageable element having a thermally imageable colorant-containing layer different from that of the first thermally imageable element forms a laserable assemblage with the receiver element having the colorant containing image of the first pigment and is imagewise exposed and separated as described above. The steps of (a) forming the laserable assemblage with a thermally imageable element having a different pigment than that used before and the previously imaged receiver element, (b) exposing, and (c) separating are sequentially repeated as often as necessary in order to build the multi-colorant-containing image of a color proof on the receiver element. The image on the receiver therefore changes as the image is built up, and the transmission of this image at the wavelength of the non-imaging laser changes as the process is repeated. Light passing through this image and reflected into the light detector, typically a position sensitive light detector, causes imaging errors, which are greatly reduced by the light attenuated layer in the receiver.

The rigidification element may then be brought into contact with, typically laminated to, the multiple colorant-containing images on the image receiving element with the last colorant-containing image in contact with the thermoplastic polymer layer. The process is then completed as described above.

Color Filters

A specific embodiment of the invention is the creation and use of a color filter element. Color filters are the subject of U.S. Pat. No. 6,242,140, Kwon et al. Color filters can be prepared utilizing two different versions of thermal imaging equipment. The first is a conventional drum type imager such as a Creo Model 3244 Spectrum Trendsetter (Creo Inc., Vancouver, Canada) equipped with a 20 W laser head operating at a wavelength of 830 nm, suitable for imaging of flexible receivers. Imaging assemblages can be exposed from the back side through the donor film. Films can be mounted using vacuum hold down to a standard plastic carrier plate clamped mechanically to the drum. Control of the laser output is under computer control to build up the desired image pattern. The desired three color image can be built up by sequentially exposing the red, green and blue donor films. The exposure order for the colors can be varied according to other system requirements (e.g. optimal exposure characteristics).

A second kind of imager (the “flatbed”) employs an identical imaging head, but based on a flatbed format rather than the Trendsetter drum format. The flatbed imager is preferred for exposure of relatively rigid, flat samples. The sample to be exposed is mounted using vacuum hold down to a translation stage positioned below the imaging head. During exposure the sample is typically translated past the imaging head at a speed of 1.0-1.2 m/s. Following the completion of each exposure pass, the imaging head is translated in the direction orthogonal to the sample translation to move a new unexposed area of film in front of the laser for the next imaging pass. This process is repeated to build up the completed exposure. As in the drum imager, the desired three color image is prepared by sequentially exposing the red, blue and green donors to the same receiver element in any order desired.

Accuracy of movement of the flatbed is important. A useful flatbed positioning system can be constructed using linear air bearings constructed using appropriate linear brushless servomotors as the drive system, and a noncontact linear encoder or laser interferometer for position feedback. Resolution will typically be as precise as 0.3 nanometers to 79 nanometers for a laser interferometer, or 4 to 1000 nanometers for a non-contact linear encoder, with an overall accuracy of plus or minus one micron, repeatability to 0.4 microns, with differential straightness and flatness of 0.5 microns per 25 millimeters and maximum deviation of plus or minus 3 microns. An appropriate translation stage system is the ABL80075 manufactured by Aerotech, Inc., Pittsburgh, Pa.

For both imaging systems, laser power is controllable and is adjusted in an iterative fashion to optimize image quality as judged by visual or instrumental inspection of the transferred image on the receiving surface.

During imaging exposure of the thermally imageable elements by the imaging laser, the ambient environment is preferably maintained from about 35 to about 45 percent relative humidity and from about 20 to about 24 degrees Centigrade.

Following the transfer of thermally imaged material such as a color filter pattern to the surface of the permanent substrate for a color filter which is typically glass or glass with a photolithographically produced mask, it is optional to add a overcoat to the surface of the color filter. The overcoat can serve to protect the thermally imaged material and to reduce light scattering due to surface roughness. In a specific embodiment, the overcoat is colorless and transparent. Various means may be employed to apply the overcoat. In a specific embodiment the overcoat may be laminated from a carrier sheet as described in more detail in an example below. Alternatively the overcoat may be applied as a liquid by conventional spin coating technologies, followed by drying to yield the final overcoat.

In a specific embodiment of the overcoat, a useful ingredient is a copolymer of methyl methacrylate, glycidyl methacrylate, n-butyl acrylate, and methacrylic acid. A useful additive in the overcoat is a base. Suitable bases are ammonia and N,N-dimethylethanolamine. Surfactants are useful ingredients in the overcoat. A specific example of a useful surfactant is a fluorosurfactant, such as CAS # [57534-45-7], ZONYL® FSA (DuPont, Wilmington, Del.). A useful carrier sheet for the overcoat is a polyester film.

Color filters can be incorporated into functional active matrix liquid crystal display devices using techniques which are well known within the liquid crystal display industry (see, for instance “Fundamentals of Active-Matrix Liquid-Crystal Displays”, Sang Soo Kim, Society for Information Display Short Course, 2001; and “Liquid Crystal Displays: Addressing Schemes and Electro-optical Effects”, Ernst Lueder, John-Wiley, 2001; and U.S. Pat. No. 5,166,026).

EXAMPLES

These non-limiting examples demonstrate the processes and products described herein wherein images of a wide variety of colors are obtained. A specific embodiment is an image which generates bars of color which fall over a mask, thereby making a color filter. Other configurations of colors in an image which are useful as a color filter are known to those skilled in the art. All percentages are weight percentages unless indicated otherwise. Sigma-Aldrich, St. Louis, Mo., is a useful source of many of the materials used here.

Glossary

SDA 2-[2-[2-Chloro-3[2-(1,3-dihydro-1,1dimethyl- 3(4sulfobutyl)-2H-benz[e]indol-2- yllidene)ethylidene[-1-cyclohexen-1-yl]- ethenyl]-1,1-dimethyl-3-(sulfobutyl)-1H- benz[e]indolium, inner salt, free acid SDA 4927 Infrared dye [CAS No. 162411-28- 1] (H.W. Sands Corp., Jupiter, FL) FSA Zonyl ® FSA fluoro surfactant; 25% solids in water and isopropanol, [CAS No. 57534-45- 7] A lithium carboxylate anionic fluoro- surfactant having the following structure: RfCH2CH2SCH2CH2CO2Li where Rf = F (CF2CF2)x and where x = 1 to 9 (DuPont, Wilmington, DE) FSD Zonyl ® FSD fluoro surfactant; 43% active ingredient in water (DuPont, Wilmington, DE) RCP-26735 Methylmethacrylate/n-butylmethacrylate (76/24) copolymer latex emulsion at 37.4% solids (DuPont, Wilmington, DE). PEG 6800 Polyethylene glycol 6800 [CAS No. 25322-68- 3], 100%, Scientific Polymer Products, Inc., Ontario, NY) PEG Polyethylene glycol 6800 [CAS No. 25322-68- 3], 100%, Scientific Polymer Products, Inc., Ontario, NY) DF110D Surfynol ® DE110D (Air Products) Zinpol ® 20 Zinpol ® 20, Polyethylene wax emulsion, 35% in water (B. F. Goodrich Company) MELINEX ® 573 4 mil clear PET base (DuPontTeijinFilms ™, a joint venture of E.I. du Pont de Nemours & Company) MELINEX ® 6442 4 mil polyethylene terephthalate film base with 670 nm dye absorber (DuPontTeijinFilms ™ , a joint venture of E.I. du Pont de Nemours & Company). The 670 nm dye is CAS # [12217-80-0], known as 1H-Naphth[2,3- f]isoindole-1,3,5,10(2H)-tetrone,4,11-diamino- 2-(3-methoxypropyl)-(9CI) (CA INDEX NAME) Base absorbance at 670 nm is 0.5 to 0.7 Absorbance units, at 830 nm is less than 0.07 Absorbance units. 30S330 Green Shade Phthalo Blue Waterborne Dispersion 40% solids (Penn Color, Inc., Doylestown, PA) 32Y144D Green Shade Yellow Waterborne Dispersion 41% solids (Penn Color, Inc., Doylestown, PA) 32Y145D Red Shade Yellow Waterborne Dispersion 40% solids (Penn Color, Inc., Doylestown, PA) 32R164D Red 32R164D pigment dispersion; 40% in water (Penn color, PA) 325168D Violet 32S168D pigment dispersion; 41% in water (Penn Color, PA) 325187D Blue 32S187D pigment dispersion; 40% in water (Penn Color, PA) Creo Model 3244 Creo Inc., Vancouver, Canada Spectrum Trendsetter MELINEX ® DuPont Teijin Films, Wilmington, DE Riston ® Model HRL-24 Roll Laminator DuPont, Wilmington. DE Wyko Model RST Plus Surface Profiler Wyko Corp., Tucson, Arizona Corning 1737 display Corning Glass Company, Corning, NY grade glass VAZO ® 67 2,2′-azobis-(2-methylbutyronitrile) Du Pont, Wilmington, DE ZONYL ® FSA fluoro surfactant; 25% solids in water and isopropanol, [CAS No. 57534-45-7] A lithium carboxylate anionic fluorosurfactant having the following structure: RfCH2CH2SCH2CH2CO2Li where Rf = F (CF2CF2)x and where x = 1 to 9. DuPont, Wilmington, DE CRONAR ® 471X polyester film, DuPont, Wilmington, DE ELVAX ® 550 ethylene vinyl acetate copolymer, DuPont, Wilmington, DE POLYSTEP B-7 Stepan Co., Northfield, IL ethylene glycol Aldrich, Milwaukee, WI monobutyl ether [111-76-2] N,N-dimethylethanol- Aldrich, Milwaukee, WI amine [108-01-0]]

Example 1

Preparation of the Thermally Imageable Compositions

This example shows the preparation of a 670 nm absorbing coatable composition and a thermally imageable element. The thermally imageable element comprises a 4 mil polyester base element (MELINEX® 573) sputtered with about 70 Å of chromium, sufficient to produce about 60% transmission of light, by CP Films (Martinsville, Va.). The metal thickness was monitored in situ using a quartz crystal and after deposition by measuring reflection and transmission of the films. This metalized base was then coated with the Magenta formula depicted in Table 1 using production equipment.

TABLE 1 Recipes for colorant-containing compositions: Ingredient Magenta Yellow Cyan Deionized Water 12,294 18,050 15,433 RCP 26735  4,326  4,133  6,941 32R164D  1,526 32S168D   19.2 32Y144D  1,321 32Y145D   257.7 30S330  1,259 32S187D   160.2 PEG   146.3   153.8   135.4 SDA 4927   53.2   48.1   50.7 DF110D   12.2 FSA   26.6   24.2   19.5 TOTAL (grams) 19,000 24,000 24,000

TABLE 2 Recipe for 670 nm absorbing coating: Ingredient Absorber Distilled Water 129.7 RCP 26735  59.4 30S330  9.5 PEG  1.1 FSD  0.3 TOTAL (grams) 200.0

Example 2

This example shows that using a 4 mil polyester MELINEX® 6442 base element with a 670 nm absorber (30S330) as part of the base element's composition allows the single and overprint focus positions to match each other. A magenta formulation equivalent to that described in Table 1 was coated onto both a non-absorbing metalized MELINEX® 573 base element and a 670 nm absorbing metalized MELINEX® 6442 base element at the coating weights listed in Table 4. The solution was metered by a pump and coated on to a web of metalized MELINEX® base element moving past a slot die applicator then transported into a forced hot air dryer. The coated web was wound on to a core then cut into sheets of a size compatible with the Creo 3244 Spectrum Trendsetter. The magenta coatings were then imaged onto a receiver using the Creo 3244 Spectrum Trendsetter producing laser generated magenta color thermal digital halftone proofs.

The results in Table 4 show that the images made with the magenta coated base element containing the 670 nm absorber had similar focus positions for single color and overprints whereas those images made from a magenta coated base element which was non-absorbing had different focus positions.

The focus position variations reported in the data of Tables 4 and 5 were considered to result from variations in colorant layer thickness and aging because several months passed between when the tests were run.

Focus position data used in these examples was collected from the computer diagnostic port of the Creo 3244 Spectrum Trendsetter.

TABLE 4 Focus Position of 670 nm absorbing MELINEX ® base Magenta Donor Focus Focus Base element Position Position (clear or Weight Coating Single Over- absorbing) mg/dm2 Absorbance Color print Clear 14.1 .36 30 55 Clear 15.5 .34 30 45 Clear 12.7 .32 30 50 Absorbing 13.9 .95 80 80 Absorbing 12.9 .95 85 85 (1) Metalized clear base element MELINEX ® 573 has .29 absorbance at 670 nm. (2) Metalized 670 nm absorbing base element has .94 absorbance at 670 nm.

Example 3

This experiment determined that using the 670 nm absorbing base element for the yellow, magenta and cyan coatings separately caused their focus positions to be about the same, which was found not to be the case without the absorber.

This example shows that using a 4 mil polyester MELINEX® 6442 base element containing a 670 nm absorber (30S330) results in the focus positions for yellow, cyan, and magenta to be close to each other or the same. The yellow, cyan, and magenta donor coatings described in Table 1 were applied to both non-absorbing metalized MELINEX® 573 and 670 nm absorbing metalized MELINEX® 6442 at the coating weights listed in Table 5. The colorant-containing coatings were then imaged onto a receiver using the Creo 3244 Spectrum Trendsetter producing laser generated magenta color thermal digital halftone proofs for the single colors.

The results in Table 5 show that the images made with each separate single color on the 670 nm absorbing MELINEX® polyester base element have the same or a similar focus position, whereas those on the non-absorbing base element vary significantly.

TABLE 5 670 nm absorbing polyester with separate colors Donor Focus Substrate Coating Position Donor (clear or Weight Position Single Color absorbing) mg/dm2 Absorbance Color magenta clear 14.03 .29  80 magenta absorbing 13.87 .84 120 cyan clear 12.6 .73  80 cyan absorbing 12.53 1.28 125 yellow clear 8.87 .289  60 yellow absorbing 8.77 .29 120 (1) Metalized clear base element MELINEX ® 573 has .28 absorbance at 670 nm. (2) Metalized 670 nm absorbing base element has .80-.88 absorbance at 670 nm.

Example 4

This example illustrates how to make a color filter and a liquid crystal display by the method of this invention. The resulting color filter is a sheet of glass with a black grid mask exposing pixel areas, the mask and pixel areas covered by a receiver layer. On the receiver layer there is a repeating image of three alternating separate transparent bands of thermally transferred material of single colors (red, blue, or green) which effectively cover all the exposed pixel areas and some portions of the black grid mask, so that light shining through any pixel in the liquid crystal display using the color filter will be filtered through the transparent colored region after travelling through the pixel defined by the absence of mask. An overcoat covers all the bands of thermally transferred material and the remaining portions of the receiver layer which do not hold any thermally transferred material. This example includes procedures for making various compositions which are useful in making the receiving layer, thermally imaged layer, or overcoat layer. Useful compositions include chain transfer agents, polymers, latexes, dispersants, and binders. A single composition such as a latex can be useful in one or more than one layer.

A permanent substrate PS-1 of Corning 1737 display grade glass with a black mask grid was used in construction of the receiver element. The glass was specified to be 0.7 mm thick with a surface with an area specified to be 12 inches by 14 inches. The black mask grid, 10 inches by 12 inches, is typical of a conventional XGA display for a color liquid crystal display of a laptop computer and was formed on the surface by conventional photolithographic techniques (e.g. U.S. Pat. No. 6,242,140 Kwon, et al.) from a vacuum deposited chrome layer of typically 1 to 2 microns in thickness. The black mask grid pitch was designed to give rectangular transparent regions 90 microns by 290 microns with opaque separation of 10 microns by 300 microns between adjacent transparent regions, ultimately resulting in three-color pixel groups designed to be 300 microns by 300 microns composed of three adjacent, differently colored pixels (red, green, and blue) of 90 microns by 290 microns.

A chain transfer agent solution used in the following latex synthesis was prepared as described by the methods of U.S. Pat. No. 5,362,826, Berge, et. al. and U.S. Pat. No. 5,324,879, Hawthorne. This chain transfer agent is an example of a macromonomer useful for regulating molecular weight of polymers produced by free-radical polymerization.

A 500-liter reactor was equipped with a reflux condenser and nitrogen atmosphere. The reactor was charged with methyl ethyl ketone (42.5 kg) and isopropyl-bis(borondifluorodimethylglyoximato) cobaltate (III) (Co III DMG) (104 g) and the contents brought to reflux. A first mixture of Co III DMG (26.0 g), methyl methacrylate (260 kg), and methyl ethyl ketone (10.6 kg) was added in a first feed to the reactor at a constant rate over a total period of 4 hours. Starting at the same time as the start of the first feed, a second mixture of VAZO® 67 (5.21 kg) and methyl ethyl ketone (53.1 kg) was added in a second feed to the reactor at a constant rate over a total period of 5 hours. After the completion of the second feed in 5 hours, the reactor contents were kept at reflux for a further 30 minutes. After cooling to ambient temperature, a 70 wt % solids solution of the chain transfer agent was obtained.

PR-1 latex of controlled molecular weight polymer resin was prepared as detailed below using the chain transfer agent solution according to the method in U.S. Pat. No. 5,773,534, Antonelli, et. al. PR-2 latex of high molecular weight polymer resin was prepared by a similar method, differing by omitting the chain transfer agent solution.

A 3-liter, round bottom flask was equipped with a condenser, addition funnel, initiating solution inlet port, mechanical stirrer, heater and temperature controller probe, with the contents maintained under a nitrogen atmosphere. The flask was charged with 700 grams of deionized water and 6.90 grams of POLYSTEP B-7. A first initiating solution of 0.40 grams ammonium persulfate in dissolved in 100 mL of deionized water was prepared. A first monomer blend of 122 grams methyl methacrylate, 4.0 grams glycidyl methacrylate, 60 grams n-butyl acrylate and 8.0 grams chain transfer agent solution was prepared and placed in the addition funnel. A second monomer blend of 122 grams methyl methacrylate, 4.0 grams glycidyl methacrylate, 60 grams n-butyl acrylate, 12.0 grams of methacrylic acid and 8.0 grams chain transfer agent solution was prepared. While stirring, the contents of the reaction flask was heated to 85 degrees Centigrade and maintained at that temperature, within a range of 3 degrees centigrade, through the following steps. Throughout the period of heating, the reaction flask contents were stirred rapidly (without generating excessive amounts of foam) in order to assure good mixing of ingredients as they were added.

The synthesis of the PR-1 latex was initiated by the first addition to the flask of 80 mL of the first initiating solution, followed within one minute by the second addition of 20 mL of the first monomer blend from the addition funnel. These two additions were complete in less than one minute. The remaining portion of first monomer blend in the addition funnel was added to the flask, beginning within two minutes, at a constant rate over a period of 60 minutes. At the end of the addition of the first monomer blend, the second monomer blend was promptly added within two minutes to the addition funnel and immediately thereafter was added to the flask at a constant rate over a period of 60 minutes total. When the addition of the second monomer blend was complete, the remaining initiating solution was promptly added in less than one minute. Stirring of the contents of the flask at about 82 to about 88 degrees Centigrade was maintained for 30 minutes after the completion of the addition of the initiating solution. Thereafter the contents of the reaction flask were cooled to ambient temperature and filtered through a fine paint strainer, (Paul N. Gardner Company, Inc. Pompano Beach, Fla., Item number ST-F 60×48 mesh) to provide PR-1 latex.

PR-1 latex had a solids weight percent content of 33.1%, particle diameter of 86 nanometers, glass transition temperature of 55 degrees Centigrade, number average molecular weight of 20,000 daltons, and weight average molecular weight of 85,000 daltons.

PR-1N latex (a neutralized latex) was provided by addition while stirring of 18 grams of a 25% solution by weight of N,N-dimethylethanolamine in water to the flask containing the PR-1 latex, after cooling and before filtration of the latex. Neutralized latex should be made no more than 24 hours before the completion of formulation, coating, and drying, to avoid premature crosslinking of the polymer.

PR-2 latex of high molecular weight polymer resin, useful for example in an image receiving layer, was prepared using the following procedure. A 3-liter, round-bottom flask was equipped with a condenser, addition funnel, mechanical stirrer, heating mantle, and temperature controller probe, with the contents maintained under a nitrogen atmosphere. The flask was charged with 700 grams of deionized water and 6.90 grams of POLYSTEP B-7. An initiating solution of 0.400 grams ammonium persulfate dissolved in 100 mL of deionized water was prepared. A first monomer blend of 96.00 grams methyl methacrylate, 4.00 grams glycidyl methacrylate, and 80.00 grams n-butyl acrylate was prepared and placed in the addition funnel. A second monomer blend of 96.00 grams methyl methacrylate, 4.00 grams glycidyl methacrylate, 80.00 grams n-butyl acrylate, and 40.00 grams methacrylic acid was prepared. While stirring, the contents of the reaction flask were heated to about 82 to about 88 degrees Centigrade and maintained at that temperature through the following steps. Throughout the period of heating, the reaction flask contents were stirred rapidly (without generating excessive amounts of foam) in order to assure good mixing of ingredients as they were added.

The synthesis of PR-2 latex was initiated by the first addition to the flask of 80 mL of the first initiating solution, followed within one minute by the second addition of 20 mL of the first monomer blend from the addition funnel. These two additions were complete in less than one minute. The remaining portion of first monomer blend in the addition funnel was added to the flask, beginning within two minutes, at a constant rate over a period of 60 minutes. At the end of the addition of the first monomer blend, the second monomer blend was promptly added within two minutes to the addition funnel and immediately thereafter was added to the flask at a constant rate over a period of 60 minutes total. When the addition of the second monomer blend was complete, the remaining initiating solution was promptly added in less than one minute. Stirring of the contents of the flask at about 82 to about 88 degrees Centigrade was maintained for 30 minutes after the completion of the addition of the initiating solution. Thereafter the contents of the reaction flask were cooled to ambient temperature and filtered through a fine paint strainer, (Paul N. Gardner Company, Inc. Pompano Beach, Fla., Item number ST-F 60×48 mesh) to provide the PR-2 latex.

PR-2N latex (a nuetralized latex) was provided by addition while stirring of 18 grams of a 25% solution by weight of N,N-dimethylethanolamine in water to the flask containing PR-2 latex, after cooling and before filtration of PR-2 latex. The pH of the neutralized PR-2N was 8.5.

PR-2 latex had a solids weight percent content of 33.4%, particle diameter of 91 nanometers, and a glass transition temperature of 32 degrees Centigrade.

Solids weight percent content was measured by putting an accurately weighed portion of about 4.8 to about 5.2 grams of latex in a tared, 5-cm diameter aluminum pan, which was dried in a 75° C. vacuum oven at about 350 to about 450 torr for 1 to 2 days. The difference in initial and final weights of the latex determines the solids weight percent content. Glass transition temperature (Tg) values reported are mid-point temperatures in degrees Centigrade from differential scanning calorimetry scans recorded according to ASTM D3418-82.

Molecular weights were measured by gel permeation chromatography (GPC) in a system calibrated with low polydispersity polymethyl methacrylate. The equipment used consisted a 2-5 mm×300 mm×7.5 mm size exclusion column, a refractive index detector (Waters, Inc., Milford, Mass., 410 Refractive Index detector); a pump, (Waters 590); and a column heater. Conditions used were: refractive Index detector internal temperature, 30° C.; column heater temperature, 30° C.; tetrahydrofuran solvent, 0.025% BHT inhibited from Omnisolv, EM Science, Gibbstown, N.J., part# TX0282,1 distilled LC grade); flow rate, 1 ml/min; Concentration, 0.1% (10 mg/10 ml). Samples were prepared by dissolving parts of the samples used for solids determination overnight with gentle shaking, and then filtering through a 0.5 um filter.

Particle size was determined by dynamic light scattering using a Brookhaven Instrument BI-9000AT digital correlator (Brookhaven Instruments, Brookhaven, N.Y.). An argon-ion laser with wavelength 488 nm and power 200 mW was used. Measurements were made at room temperature with scattering angle 60°. The samples were diluted 200 μL into 20 mL water then again 100 μL into 20 mL water, and then filtered with 0.45 micron filter. The results are reported as diameter (particle size) in nm units. For general discussions of the determination of particle sizes by quasielastic light scattering, see Paint and Surface Coatings: Theory and Practice, ed. By R. Lombourne, Ellis Horwood Ltd., West Sussex, England, 1987, pp. 296-299, and The Application of Laser Light Scattering to the Study of Biological Motion, ed. By J. C. Earnshaw and M. W. Steer, Plenum Press, NY, 1983, pp. 53-76.

DBC-1 pigment dispersant solution was made by group transfer polymerization techniques as described in U.S. Pat. No. 5,772,741, Spinelli to form a block copolymer of benzyl methacrylate (BZMA) and methacrylic acid (MAA) as follows: a 12-liter flask was equipped with a mechanical stirrer, thermometer, nitrogen inlet, drying tube outlet, and addition funnels. Tetrahydrofuran, 3750 gm, and p-xylene, 7.4 gm, were charged to the flask. The catalyst tetrabutylammonium m-chlorobenzoate, 3.0 ml of a 1.0M solution in acetonitrile, was then added to the flask. Initiator, 1,1-bis(trimethylsiloxy)-2-methyl propene, 291.1 gm (1.25M) was added to the flask. Feed I of tetrabutyl ammonium m-chlorobenzoate, 3.0 ml of a 1.0 M solution in acetonitrile, was started at 0.0 minutes and completely added at a constant rate over 180 minutes. Feed II of trimethylsilyl methacrylate, 1975 gm (12.5M) was started at 0.0 minutes and completely added at a constant rate over 35 minutes. One hundred minutes after Feed II was completed (over 99% of the monomers had reacted as analyzed by gas chromatography), Feed III of benzyl methacrylate, 2860 gm (16.3M) was started and completely added at a constant rate over 30 minutes.

At 400 minutes, 720 gm of methanol were added to the flask and a distillation of the flask contents was begun. During the first stage of distillation, 1764.0 gm of material were removed. Then more methanol (304.0 gm) was added to the flask and an additional 2255.0 gm of distilled material were distilled out. The flask contents were cooled to ambient temperature and removed. The DBC-1 solids content was 49.7% weight solids. The polymer had a nominal composition of BZMA//MAA 13//10. It had a number average molecular weight of 3,200 daltons as determined by gel permeation chromatography.

PDC-R2 pigment chip was made on a conventional two-roll mill using 180.0 grams of Clariant PV FAST RED B (a brand of Pigment Red 149 available from Clariant, Charlotte, N.C.), 240.0 grams of DBC-1, and 53.0 grams of diethylene glycol. The two-roll mill rollers were heated to 150° F. at a slow roll. The ingredients were allowed process for 5 to 10 minutes to drive off low-boiling solvents. The fast roll was cooled to force transfer to the slow roll and the mixture was processed for 45 minutes. The pigment dispersion chip product was pliable without being sticky. PDC-R2 was 89.0% solids by weight.

The pigment dispersion chip PDC-R2 (140.45 grams, crushed) was mixed on a conventional high speed disperser with 13.78 g (99% purity) dimethylaminoethanol and 160 g deionized water at 2000 rpm for 2 hours. After slowing the stirrer substantially, deionized water was added and mixed to bring the total weight of the pigment dispersion to 500 grams of product, designated PD-R2, a red pigment dispersion.

Waterborne pigment dispersions of suitable characteristics for making a thermal imaging element in a color filter can be made with other binders being used as pigment dispersants, for example commercially available polymers, oligomers, waxes, or natural products which are pigment dispersants. The dispersions listed below are specific examples of useful dispersions. A suitable blue aqueous pigment dispersion PD-B1 of Pigment Blue 156 at 33.7 weight percent pigment and pigment to binder ratio of 2 was used (PENN COLOR 32S195, Penn Color, Pa.). A suitable green aqueous pigment dispersion PD-G1 of Pigment Green 36 at 35 weight percent pigment and pigment to binder ratio of 2.3 was used (PENN COLOR 32G200, Penn Color, Pa.). A suitable aqueous pigment dispersion PD-R3 of Pigment Red 254 at 24 weight percent pigment and pigment to binder ratio of 1.5 was used (PENN COLOR 32R238D, Penn Color, Pa.). A suitable red aqueous pigment dispersion PD-R1 of Pigment Red 177 at 35 weight percent pigment and pigment to binder ratio of 3.5 was used (PENN COLOR 32R194, Penn Color, Pa.). A suitable aqueous pigment dispersion PD-V1 of Pigment Violet 23 at 34 weight percent pigment and pigment to binder ratio of 2.3 was used (PENN COLOR 32S212, Penn Color, Pa.). A suitable yellow aqueous pigment dispersion PD-Y2 of Pigment Yellow 74 at 25 weight percent pigment and pigment to binder ratio of 1.5 was used (PENN COLOR 32Y213D, Penn Color, Pa.). A suitable yellow aqueous pigment dispersion PD-Y1 of Pigment Yellow 83 at 28 weight percent pigment and pigment to binder ratio of 2.3 was used (PENN COLOR 32Y145D, Penn Color, Pa.). Other suitable dispersions can be used.

The pigment dispersions were used to prepare color filter thermally imageable layer formulations. Red thermally imageable layer formulation DLF-1R was prepared with 308.6 grams PD-R1, 4263.2 grams PD-R2, 2647.6 grams PR-1N latex, 43.2 grams ZONYL® FSA, 37.2 grams of SDA [CAS # 162411-28-1], and 10701.3 grams deionized water. DLF-1R was coated on the metallized side of MELINEX® 6442 metallized with chromium to 50% transmittance, to achieve a dried coating weight of 18 mg per decimeter squared for the color filter thermally imageable element CF-1R. The optical density of CF-1R versus an air reference was 2.4 absorbance units at 473 nm and 1.45 absorbance units at 551 nm.

Blue thermally imageable layer formulation DLF-1B was prepared with 2131.2 grams PD-B1, 111.2 grams PD-V2, 2913.2 grams PR-1N latex, 43.2 grams ZONYL® FSA, 37.2 grams of SDA [CAS # 162411-28-1], and 12764.0 grams deionized water. DLF-1B was coated on the metallized side of MELINEX® 473 metallized with chromium to 50% transmittance, to achieve a dried coating weight of 10.6 mg per decimeter squared for the color filter thermally imageable element CF-1B. The optical density of CF-1B versus an air reference was 2.03 absorbance units at 610 nm and 1.99 absorbance units at 763 nm.

Green thermally imageable layer formulation DLF-1G was prepared with 1265.1 grams PD-G1, 388.8 grams PD-Y2, 1114.5 grams PR-1N latex, 24.0 grams ZONYL® FSA, 20.6 grams of SDA [CAS # 162411-28-1], and 7186.9 grams deionized water. DLF-1G was coated on the metallized side of MELINEX® 473 metallized with chromium to 50% transmittance, to achieve a dried coating weight of 16.1 mg per decimeter squared for the color filter thermally imageable element CF-1G. The optical density of CF-1G versus an air reference was 1.73 absorbance units at 655 nm.

The color filter thermally imageable layer formulations were prepared in a stirred 40 liter stainless steel vessel in air by adding sequentially the specified amounts of water, ZONYL® FSA, SDA, the latex (if neutralized, then freshly prepared within 24 hours), and the pigment dispersions. The thermally imageable layer formulations were stirred for one to two days before filtration through a 5-micron filter. The thermally imageable layer formulations were coated onto the specified thermally imageable bases (metallized MELINEX® films) and immediately dried at temperatures which increased from an initial value of 37 to 40 degrees Centigrade and ended at 64 to 68 degrees Centigrade in a period of 4 to 6 minutes, obtaining the specified coating weight per unit area as recorded for the resulting color filter thermally imageable element comprising a color filter thermally imageable layer on the color filter thermally imageable base. Using these techniques, color filter thermally imageable elements CF-1R, CF-1B, and CF-1G were made.

A receiver layer coating composition RCC-1 was formulated by the combination of the approximately 12574.0 grams of PR-2 latex, 43.2 grams of ZONYL® FSA, 109.6 grams of N,N-dimethylethanolamine, 1106.0 grams of ethylene glycol monobutyl ether, and 22186.0 grams of distilled water which were well mixed. A receiver support, 6.5 mils thick composed of 4 mil thick CRONAR® 471X polyester film and 2.5 mil ELVAX® 550 ethylene vinyl acetate copolymer, was coated on the ELVAX® 550 surface with the receiver layer coating composition RCC-1 and dried over a period of 4 to 6 minutes starting at 37 to 40 degrees Centigrade and ending at 64 to 68 degrees Centigrade to obtain a dried coating thickness of about 30 milligrams per square decimeter of dry RCC-1 on the coated film. The resulting coated film is termed receiver layer carrier RLC-1.

An overcoat composition OC-1 was prepared by mixing 86.62 grams of PR-1N latex, 0.14 grams ZONYL® FSA, 7.34 grams ethylene glycol monobutyl ether, and 5.89 grams deionized water. An overcoat composition OC-2 was prepared by mixing 111.75 grams of PR-1 latex, 0.50 grams ZONYL® FSA, 12.50 grams ethylene glycol monobutyl ether, 2.79 grams of 3 weight % aqueous ammonium hydroxide and 72.46 grams deionized water. An overcoat carrier film OCF-1 was made with an overcoat carrier film base of MELINEX® 573 (4 mil) film which was coated with OC-1 using a #12 Meyer rod and dried for 12 minutes at 50 degrees Centigrade to give a final dried coating weight of 82 mg/dm2. An overcoat carrier film OCF-2 was made with an overcoat carrier film base of MELINEX® 573 (4 mil) film which was coated with OC-2 using a #8 Meyer rod and dried for 18 minutes at 45 degrees Centigrade to give a final dried coating weight of 3 mg/dm2.

Just prior to addition of the receiver layer carrier RLC-1 to the permanent substrate PS-1, the permanent substrate PS-1 was cleaned. Surface debris was first removed by blowing clean high-pressure ionized nitrogen gas using a high-performance ionizing air gun for electronics manufacturing and cleanroom applications, with a 0.2 micron filter at the exit (Top Gun Ionizing Air Gun, Model 4005105, Simco Co., Hatfield, Pa.,). The permanent substrate PS-1 was then washed with a soap (Micro-90 brand soap, International Products Corp., Burlington, N.J.), and rinsed sequentially with water, isopropanol and finally with deionized water. The glass was dried under a nitrogen purge. Immediately prior to application of the receiver carrier film RLC-1, the permanent substrate PS-1 was again cleaned with high-pressure ionized nitrogen gas.

The lamination of receiver carrier film RLC-1 to the chrome-containing surface of the permanent substrate PS-1 was carried out using a Riston® Model HRL-24 Roll Laminator (DuPont). After removing the cover sheet, a sheet of RLC-1 was placed with the RCC-1 coated side in contact with the cleaned surface of the permanent substrate PS-1 (the surface with the preformed opaque chrome mask). Lamination was carried out with the rollers heated to 97 degrees Centigrade at a speed of 0.2 meters/minute. The laminator air feed was adjusted to a pressure of 40 psi. Following lamination, the laminated assembly was allowed to cool to ambient temperature. The resulting protected receiver element of the permanent substrate, receiver layer, and receiver support is converted to a imageable-element-ready receiver element by removal of the receiver support (6.5 mils thick) by peeling it away from the receiver element. The removal of the receiver support was generally carried out immediately prior to imaging in order to protect the receiver layer surface from contamination in handling. After removal of the receiver support, the surface of the receiver layer on the receiver element was very smooth. Measurement of the surface roughness of the receiver layer with a Wyko Model RST Plus Surface Profiler (Wyko Corp., Tucson, Ariz.) showed an average roughness (Ra) of 28 nm over a measurement area of 1.08 square millimeters.

A Creo Model 3244 Spectrum Trendsetter (Creo, Vancouver, Canada) was modified to enable it to imagewise expose a flexible or rigid laser-imageable assemblage held on a flat vacuum-hold-down translation stage, analogously to exposure of a flexible laser imageable assemblage held on the drum of the unmodified Creo Model 3244 Spectrum Trendsetter. The flat vacuum-hold-down table is Model ABL80075 from Aerotech, Inc., Pittsburg, Pa.

The construction of the rigid laser-imageable assemblage began with the protected receiver element held down by vacuum on the flat vacuum-hold-down translation stage so as to expose the receiver support. The receiver support was then peeled away to expose the receiver element surface. The receiver element surface was then contacted by the thermally imageable layer surface of a color filter thermally imageable element. The color filter thermally imageable element measures about 17 inches by 17 inches and was placed so that a frame of about 2.5 inches by 1.5 inches was evenly formed around the 12 inch by 14 inch receiver element on the permanent substrate on the flat vacuum-hold-down translation stage, the frame consisting of the outter most portion of the color filter thermally imageable element held directly to the flat vacuum-hold-down translation stage. The vacuum-hold-down translation stage evacuated air from between the receiver element and the color filter thermally imageable element to provide intimate contact between the two surfaces in contact, thereby forming the completed laser imageable assemblage ready for imaging.

Translation of the translation stage is capable of moving the rigid laser imageable assemblage perpendicular to the designed direction of imaging head translation while keeping the distance from the imaging head to the rigid laser imageable assemblage practically constant so that imaging can occur over the entire surface of the assemblage at a nearly constant separation and laser focus controlled by the control mechanisms of the modified Creo Model 3244 Spectrum Trendsetter using the non-imaging laser and the light detector.

Imaging of the laser imageable assemblage on the modified Creo Model 3244 Spectrum Trendsetter produced an imaged assemblage by standard exposure procedures. The imaging procedure was used to transfer by portions the color filter thermally imageable layer so that each 90 by 290 micron window designated to receive the color filter thermally imageable layer was well covered by a imaged band designed to be 96 microns wide centered over the 90 micron wide window which extended over the many contiguous pixels of the single color being transferred. Many such bands were used in parallel to cover all the necessary pixels on the permanent substrate PS-1.

Removal of the color filter thermally imageable element from the imaged assemblage on the flat vacuum-hold-down translation stage removed the unexposed color filter thermally imageable layer portions with the base element, leaving on the stage a first imaged receiver element which included the color filter thermally imageable layer portions which were exposed to the laser light by the imaging process accomplished by the laser.

The color filter thermally imageable element can be removed from the imaged assemblage on the flat vacuum-hold-down translation stage using a specific method with a rod about 18 inches long and about 1.5 inches in diameter. Along the length of the edge of one of the 17-inch sides of the exposed color filter thermally imaged element, the first 1.5 inch portion of the exposed color filter thermally imaged element was removed from the vacuum hold down table and passed tightly over the curvature of the rod. The rod is then rolled across the remaining approximate 15.5 inches of the exposed color filter thermally imaged element at a nearly constant rate of speed over a period of about twenty seconds while maintaining the color filter thermally imaged element in tight contact with the rod over about one quarter to two thirds of the circumference of the rod. The rod is aligned so that exposed pixels of all three colors in a row of pixel triplets being exposed by the rolling are completely separated from the exposed color filter thermally imageable element at about the same time, rather than sequentially for all pixels of each separate color of a triplet. In other words, when the peeling is halfway done in about 10 seconds, essentially each imaged band on the receiver element is also halfway separated from the unimaged portions of the exposed thermally imaged element, rather than half the imaged bands being completely separated and half the imaged bands being completely unseparated.

The first imaged receiver element is itself a receiver element which was combined with an unimaged color filter thermally imageable element of a second color to give a new laser imageable assemblage ready for imaging which was held on the flat vacuum-hold-down translation stage, following the methods stated above. The imaging step was carried out to form a second receiver element now having two distinct sets of bands from distinct imaging steps, and repeated a third time to form a third exposed receiver element with a total of three color filter thermally imageable elements having transferred exposed color filter imageable layer portions which were exposed to the laser light, always using the original receiver element on the permanent substrate to produce a three-color color filter, using the color filter thermally imageable elements and exposure conditions described below.

The sequential steps were carried out using CF-1B, CF-1G, and CF-1R color filter thermally imageable elements to produce a three-color color filter CF-1. For the imaging of the assemblage including unimaged CF-1B, laser power was set to 5.50 watts, surface depth was set to 85 microns, swath width was set to 958 microns, and writing velocity was set to 1.2 meters per second. For the next imaging of the assemblage including unimaged CF-1G, laser power was set to 5.75 watts, surface depth was set to 75 microns, swath width was set to 958 microns, and writing velocity was set to 1.2 meters per second. For the final imaging of the assemblage including unimaged CF-1R, laser power was set to 6.25 watts, surface depth was set to 120 microns, swath width was set to 958 microns, and writing velocity was set to 1.2 meters per second.

Laser power, surface depth, swath width, and writing velocity are laser head control parameters which are set in the controllers of the Creo Model 3244 Spectrum Trendsetter.

A laminated color filter TCF-1 was made by lamination of OCF-1 to the three-color color filter CF-1. The overcoated side of a 12 inch by 14 inch piece of overcoat carrier film OCF-1 was brought into contact with the imaged side of color filter CF-1 and laminated to it in a Tetrahedron Model MTP13 vacuum press laminator. A lamination stack was constructed of the following flat layers in order: a first 0.125 inch thick stainless steel plate, a first sheet of TEFLON®, a first sheet of fiber reinforced rubber, a first sheet of MYLAR® polyester film, the color filter CF-1, the overcoat carrier film contacting the color filter CF-1 with the overcoat contacting the imaged transferred thermally imageable layer, a second sheet of MYLAR® polyester film, a second sheet of fiber reinforced rubber, a second TEFLON® sheet, and a second 0.125 inch thick stainless steel plate.

The lamination stack was placed in the chamber of the vacuum press laminator and the sample chamber atmosphere was evacuated to less than 5 torr. After evacuation, a series of nine venting cycles of a small portion of air to raise the atmospheric pressure of the chamber to about 100 to about 400 torr was carried out to remove any trapped air between the overcoat carrier film and the color filter. Lamination was then carried out at a temperature of 110 degrees Centigrade and a pressure of about 55 to about 65 pounds per square inch exerted on the lamination stack by the piston of the press for 60 minutes.

An annealed color filter ACF-1 was made from the laminated color filter TCF-1 by heating TCF-1 at 200 degrees Centigrade in air for 60 minutes.

ACF-1 was incorporated in an active matrix liquid crystal display LCD-1 by standard techniques.

Example 5

This example shows the benefit of the invention in the processing of a red thermally imageable element imaged onto a flexible receiver element suitable for a color filter. The general techniques introduced in the previous examples are used unless otherwise specified.

PR-3 latex of high molecular weight polymer resin was prepared using the following procedure. A 3-liter, round-bottom flask was equipped with a condenser, addition funnel, mechanical stirrer, heating mantle, and temperature controller probe, with the contents maintained under a nitrogen atmosphere. The flask was charged with 700 grams of deionized water and 6.90 grams of POLYSTEP B-7. An initiating solution of 0.400 grams ammonium persulfate dissolved in 100 mL of deionized water was prepared. A first monomer blend of 140.00 grams methyl methacrylate, 4.00 grams glycidyl methacrylate, and 50.00 grams n-butyl acrylate was prepared and placed in the addition funnel. A second monomer blend of 140.00 grams methyl methacrylate, 4.00 grams glycidyl methacrylate, 50.00 grams n-butyl acrylate, and 12.00 grams methacrylic acid was prepared. While stirring, the contents of the reaction flask were heated to about 82 to about 88 degrees Centigrade and maintained at that temperature through the following steps. Throughout the period of heating, the reaction flask contents were stirred rapidly (without generating excessive amounts of foam) in order to assure good mixing of ingredients as they were added.

The synthesis of PR-3 latex was initiated by the first addition to the flask of 80 mL of the first initiating solution, followed within one minute by the second addition of 20 mL of the first monomer blend from the addition funnel. These two additions were complete in less than one minute. The remaining portion of first monomer blend in the addition funnel was added to the flask, beginning within two minutes, at a constant rate over a period of 60 minutes. At the end of the addition of the first monomer blend, the second monomer blend was promptly added within two minutes to the addition funnel and immediately thereafter was added to the flask at a constant rate over a period of 60 minutes total. When the addition of the second monomer blend was complete, the remaining initiating solution was promptly added in less than one minute. Stirring of the contents of the flask at about 82 to about 88 degrees Centigrade was maintained for 30 minutes after the completion of the addition of the initiating solution. Thereafter the contents of the reaction flask were cooled to ambient temperature and filtered through a fine paint strainer, (Paul N. Gardner Company, Inc., Pompano Beach, Fla., Item number ST-F 60×48 mesh) to provide PR-3 latex. PR-3 latex had a solids weight percent content of 33.5%, particle diameter of 92 nanometers, and a glass transition temperature of 72 degrees Centigrade.

PR-4 latex of high molecular weight polymer resin was prepared using the following procedure. A 3-liter, round-bottom flask was equipped with a condenser, addition funnel, mechanical stirrer, heating mantle, and temperature controller probe, with the contents maintained under a nitrogen atmosphere. The flask was charged with 700 grams of deionized water and 6.90 grams of POLYSTEP B-7. An initiating solution of 0.400 grams ammonium persulfate dissolved in 100 mL of deionized water was prepared. A first monomer blend of 110.00 grams methyl methacrylate, 4.00 grams glycidyl methacrylate, and 80.00 grams n-butyl acrylate was prepared and placed in the addition funnel. A second monomer blend of 110.00 grams methyl methacrylate, 4.00 grams glycidyl methacrylate, 80.00 grams n-butyl acrylate, and 12.00 grams methacrylic acid was prepared. While stirring, the contents of the reaction flask were heated to about 82 to about 88 degrees Centigrade and maintained at that temperature through the following steps. Throughout the period of heating, the reaction flask contents were stirred rapidly (without generating excessive amounts of foam) in order to assure good mixing of ingredients as they were added.

The synthesis of PR-4 latex was initiated by the first addition to the flask of 80 mL of the first initiating solution, followed within one minute by the second addition of 20 mL of the first monomer blend from the addition funnel. These two additions were complete in less than one minute. The remaining portion of first monomer blend in the addition funnel was added to the flask, beginning within two minutes, at a constant rate over a period of 60 minutes. At the end of the addition of the first monomer blend, the second monomer blend was promptly added within two minutes to the addition funnel and immediately thereafter was added to the flask at a constant rate over a period of 60 minutes total. When the addition of the second monomer blend was complete, the remaining initiating solution was promptly added in less than one minute. Stirring of the contents of the flask at about 82 to about 88 degrees Centigrade was maintained for 30 minutes after the completion of the addition of the initiating solution. Thereafter the contents of the reaction flask were cooled to ambient temperature and filtered through a fine paint strainer, (Paul N. Gardner Company, Inc., Pompano Beach, Fla., Item number ST-F 60×48 mesh) to provide PR-4 latex. PR-4 latex had a solids weight percent content of 33.4%, particle diameter of 94 nanometers, and a glass transition temperature of 39 degrees Centigrade.

RCC-2 image receiving layer composition was formulated by the combination of 2607.6 grams of PR-3 latex, 3910.8 grams of PR-4 latex, 36.0 grams of ZONYL® FSA, 90 grams of a solution of 10% by weight of N,N-dimethylethanolamine in distilled water, 900.0 grams of ethylene glycol monobutyl ether, and 10455.6 grams of distilled water which were well mixed. The receiver support was a film 5.25 mils thick composed of 4 mil thick CRONAR® polyester film upon which was coated a 1.25 mil layer composed of 98.75% white Elvax® 550 chip (whose composition was 95% Elvax® 550/5% rutile titanium dioxide) and 1.25% blue Elvax® chip (whose composition was 98% Elvax® 550/2% Phthalocyanine Pigment Blue 15:3). RCC-2 was applied on the Elvax® side of the film and dried over a period of 4 to 6 minutes starting at 37 to 40 degrees Centigrade and ending at 64 to 68 degrees Centigrade to obtain a dried coating thickness of about 12.9 milligrams per square decimeter of dry RCC-2 on the reciever base. After drying of the RCC-2, the RCC-2-coated surface of the freshly coated receiver element was laminated to OSM Matte Polyethylene film (Tredegar Co., New Bern, N.C.) at a lamination pressure of 90 psi, the polyethylene film serving as a cover sheet and source of controlled roughening. The resulting coated, laminated film is termed RFC-2.

A color filter thermally imageable element CF-3R was made by the techniques described above for CF-1R. CF-3R utilized a pigment composition of 85.7% Pigment Red 149 and 14.3% Pigment Red 177, in comparison to 86.0% Pigment Red 149 and 14.0% Pigment Red 177 used for CF-1R. The color filter thermally imageable element CF-R3 contained approximately 35% red pigment (by weight) in the themally imageable layer which was present in the amount of 16.8 milligrams per decimeter squared on the base element. The thermally imageable layer was on the metal side of a base element with a coating of chromium metal to a thickness sufficient to give 50% transmission of 830 nm light. The chromium was applied to a film base containing blue dye (4 mil thick MELINEX® 6442). The thermally imageable element was imaged onto RFC-2 as a receiver element on the RCC-2 coated side after removal of the polyethylene coversheet, using the Creo Model 3244 Spectrum Trendsetter. The surface reflectivity of the thermally imageable element was determined using the Creo Model 3244 Spectrum Trendsetter manufacturer's standard procedure as a value of 0.36 with a standard deviation of measurement of 0.02. To characterize the films imaging performance a series of 209 exposure variations were made on different regions of the thermally imageable element using a color filter image for testing purposes. The initial setting used was a laser power of 5 units, a drum speed of 80 rotations per minute, and 5058 dot per inch printing. The setting of surface depth used for the writing laser was varied from 50 units to 150 units in 11 equal increments of 10 units in a pattern along the drum. At each setting of surface depth, the power setting of the writing laser was varied from 5.0 units to 9.5 units in 19 equal increments of 0.25 units in a pattern around the drum. All exposures completed successfully (no focus errors of any kind were encountered). The final product is a red color filter.

Comparative Example 6

A comparative red color filter of similar composition to Example 5 was prepared with the color filter thermally imageable layer on a color filter base element of 50% transmission chromium on 4 mil thick colorless MELINEX® 573, an essentially transparent film with no blue dye. A color filter thermally imageable element CF-4R was made by the techniques described above for CF-1R. CF-4R utilized a pigment composition of 82.9% Pigment Red 149 and 17.1% Pigment Red 177. The color filter thermally imageable element CF-R4 contained approximately 35% red pigment (by weight) in the themally imageable layer which was present in the amount of 15.4 milligrams per decimeter squared on the base element. The thermally imageable element CF-R4 was imaged on the Creo Model 3244 Spectrum Trendsetter using the same type of receiver element as in Example 5. Determination of the surface reflectivity of the comparative donor film gave a value of 0.51 with a standard deviation of measurement of 0.11. The more than four-fold higher standard deviation of the surface reflectivity measurement for the comparative donor in comparison to Example 5 is not indicative of poorer film quality, but rather is due to partial reflection of the autofocus laser from more than one surface which leads to highly variable reflectivity values. This high variability of surface reflectivity is extremely undesirable for proper operation of the Trendsetter. In a manner similar to that described for Example 5, the comparative sample was exposed with a series of 208 exposure variations using the Creo Model 3244 Spectrum Trendsetter. The setting of surface depth used for the writing laser was varied from 0 units to 120 units in 13 equal increments of 10 units in a pattern along the drum. At each setting of surface depth, the power setting of the writing laser was varied from 5.0 units to 9.5 units in 16 equal increments of 0.30 units in a pattern around the drum. Of the 208 exposures, 177 failed to plot due to focus errors (85% failure rate). The resulting product is a red color filter. 

What is claimed is:
 1. A color filter made by a process for adjusting the focus of an imaging laser for imaging a thermally imageable element having a thermally imageable layer comprising the steps of: (a) providing an imaging unit having a non-imaging laser and an imaging laser, the non-imaging laser having a light detector which is in communication with the imaging laser; (b) contacting a receiver element with the thermally imageable element in the imaging unit, the thermally imageable element comprising a light attenuated layer; (c) actuating the non-imaging laser to expose the thennally imageable element and the receiver element to an amount of light energy sufficient for the light detector to detect the amount of light reflected from the light attenuated layer of the thermally imageable element and the receiver element; (d) actuating the imaging laser to focus the imaging laser in order to imagewise expose the thermally imageable element to an amount of light energy sufficient for imagewise transfer of the thermally imageable layer to the receiver element, the focus of light energy being determined by the amount of light reflected from the light attenuated layer of the thermally imageable element and communicated to the imaging laser by the light detector; and (e) separating the thermally imageable element from the receiver element to form a color filter comprising the receiver element with the imagewise exposed areas of the thermally imageable layer transferred thereto.
 2. The color filter of claim 1 wherein the thermally imageable element comprises a base element and a thermally imageable layer, wherein the base element is the light attenuated layer.
 3. The color filter of claim 1 wherein the light attenuated layer comprises a base element having a rough surface.
 4. The color filter of claim 1 wherein the light attenuated layer comprises a light attenuating agent.
 5. The color filter of claim 4 wherein the light attenuating agent is selected from an absorber, a diffuser and mixtures thereof.
 6. The color filter of claim 5 wherein the absorber is a blue phthalocyanine pigment.
 7. The color filter of claim 5 wherein the absorber is carbon black.
 8. The color filter of claim 5 wherein the diffuser is titanium dioxide.
 9. The color filter of claim 5 wherein the light attenuating agent is a mixture of a blue phthalocyanine pigment and titanium dioxide.
 10. The color filter of claim 1 wherein the thermally imageable layer comprises a color pigment.
 11. The color filter of claim 1 wherein the non-imaging laser emits light at a wavelength ranging from about 300 nm to about 1500 nm.
 12. A liquid crystal display comprising a color filter made by a process for adjusting the focus of an imaging laser for imaging a thermally imageable element having a thermally imageable layer containing color pigment comprising the steps of: (a) providing an imaging unit having a non-imaging laser and an imaging laser, the non-imaging laser having a light detector which is in communication with the imaging laser; (b) contacting a receiver element with the thermally imageable element in the imaging unit, the thermally imageable element comprising a light attenuated layer; (c) actuating the non-imaging laser to expose the thermally imageable element and the receiver element to an amount of light energy sufficient for the light detector to detect the amount of light reflected from the light attenuated layer of the thermally imageable element and the receiver element; (d) actuating the imaging laser to focus the imaging laser in order to imagewise expose the thermally imageable element to an amount of light energy sufficient for imagewise transferring the thermally imageable layer containing color pigment to the receiver element the focus of light energy being determined by the amount of light reflected from the light attenuated layer of the thermally imageable element and communicated to the imaging laser by the light detector; (e) separating the thermally imageable element from the receiver element to form a color filter comprising the receiver element with the imagewise exposed areas of the thermally imageable layer containing the color pigment transferred thereto; and (f) incorporating the color filter into a liquid crystal display device to form a liquid crystal display comprising the color filter.
 13. The liquid crystal display of claim 12 wherein the thermally imageable layer comprises a pigment and the light attenuated layer comprises a blue phthalocyanine, titanium dioxide, carbon black or a mixture of two or more thereof.
 14. A process for making a color filter comprising the steps of: (a) providing an imaging unit having a non-imaging laser and an imaging laser, the non-imaging laser having a light detector which is in communication with the imaging laser; (b) contacting a receiver element with the thermally imageable element in the imaging unit, the thermally imageable element comprising a light attenuated layer and a thermally imageable layer; (c) actuating the non-imaging laser to expose the thermally imageable element and the receiver element to an amount of light energy sufficient for the light detector to detect the amount of light reflected from the light attenuated layer of the thermally imageable element and the receiver element; (d) actuating the imaging laser to focus the imaging laser in order to imagewise expose the thermally imageable element to an amount of light energy sufficient for imagewise transfer of the thermally imageable layer to the receiver element, the focus of light energy being determined by the amount of light reflected from the light attenuated layer of the thermally imageable element and communicated to the imaging laser by the light detector; and (e) separating the thermally imageable element from the receiver element to form a color filter comprising the receiver element with the imagewise exposed areas of the thermally imageable layer transferred thereto.
 15. The process of claim 14 wherein the thermally imageable layer comprises a pigment.
 16. The process of claim 14 wherein the light attenuated layer comprises an absorber, a diffuser or a mixture thereof.
 17. The process of claim 14 wherein the light attenuated layer comprises a blue phthalocyanine, titanium dioxide, carbon black or a mixture of two or more thereof.
 18. A process for making a liquid crystal display comprising the steps of: (a) providing an imaging unit having a non-imaging laser and an imaging laser, the non-imaging laser having a light detector which is in communication with the imaging laser; (b) contacting a receiver element with the thermally imageable element in the imaging unit, the thermally imageable element comprising a light attenuated layer and a thermally imageable layer; (c) actuating the non-imaging laser to expose the thermally imageable element and the receiver element to an amount of light energy sufficient for the light detector to detect the amount of light reflected from the light attenuated layer of the thermally imageable element and the receiver element; and (d) actuating the imaging laser to focus the imaging laser in order to imagewise expose the thermally imageable element to an amount of light energy sufficient for imagewise transfer of the thermally imageable layer to the receiver element the focus of light energy being determined by the amount of light reflected from the light attenuated layer of the thermally imageable element and communicated to the imaging laser by the light detector; (e) separating the thermally imageable element from the receiver element to form a color filter comprising the receiver element with the imagewise exposed areas of the thermally imageable layer transferred thereto; (f) incorporating the color filter into a liquid crystal display device to form a liquid crystal display comprising the color filter.
 19. The process of claim 18 wherein the thermally imageable layer comprises a pigment.
 20. The process of claim 18 wherein the light attenuated layer comprises a blue phthalocyanine, titanium dioxide, carbon black or a mixture of two or more thereof. 